I am not a rebreather diver but everyone I know that is says..../
You apparently don't know me. But you're mistaken in a few areas (as are the folks you do know) when it comes to sidemount rebreathers.
I am seeing these advertised as easy to dive and the greatest thing since sliced bread.
And from above
/...sidemount rebreathers are really tricky to dive due to the single counter lung.
Let's start by saying not all sidemount rebreathers have a single counter lung. Do some research.
Not that it matters...
I've been diving a KISS Sidekick for about a year now, and I have to say it really is pretty easy to dive - provided you are already a proficient sidemount cave diver. You'll want to take a technical CCR course with it, rather than just a short OW oriented course, and you'll want put in 10-20 hours on the unit before you even think about venturing into a cave, and once in the cave, you'll be well advised to restrict yourself to intro level dives for the first 40 hours or so. But it's not difficult to dive, and failures are easy to manage.
I keep hearing the issue with a single counter lung, but I have to say I just don't see the problem. The Sidekick is very flood tolerant, can be recovered from a nearly total flood, and if the unit is properly positioned you'll hear water gurgling in the exhale tower area (right next tot he OPV) long before you've got enough water in the unit to cause a problem, and if you've got water in the system, you can place the OPV at the low spot in the system, hit the ADV paddle and remove the water.
Assuming you had a counter lung failure where you exhaled and then had no gas to inhale due to the single counter lung design, you just need to go to your bailout reg bungeed under your chin. It's no different than failing to get your next breath on OC with a DIR hose configuration. There doesn't seem to be a great deal of worry about that.
/...are being sold to cave divers who are no where near the level where they actually need them.
What level is that exactly? 300' Eagles Nest dives? How about a much more sedate dive to Hendley's Castle or lower Lower Orange Grove?
Or are you suggesting it's all about penetration distance and unless you're doing 5000 foot plus penetrations there's no need?
You need to consider some of the advantages of a CCR before you define the "suitable" applications for a CCR.
CCR offers substantial advantage in decompression even at 90-100' depths. For example, a fairly short dive in Ginnie that might have an initial deco stop of 2 minutes at 20' on a CCR running a set point of 1.2 may have an initial deco stop of 2 minutes at 40 feet, with commensurately longer shallower stops.
Consider a dive in a low, tight and very silty side mount passage where you encounter old and buried line. Low viz is a given and if you have to stop and repair the line, near zero viz is a near certainty. That becomes a much riskier dive on OC where you have limited gas and limited time. And it becomes much more stressful on exit, if you encounter broken line that you have to fix, especially if you are racking up excess deco, in addition to cutting into your reserve gas. The resulting time pressure can lead to more pressure to exit faster, with a sloppier exit and potentially diver errors.
Let's also consider a dive up the Water Source tunnel, a dive to the Crypt, a dive to poke around those cool rooms and lines off the line to Challenge, a dive to Woody's Room, or perhaps a dive past the second T in the Spring Tunnel - all in the very touristy Peacock system. Those are normally dives that require hauling a stage, and in some cases a pair of stages. All of them can be done by dropping just a single stage of extra bailout gas per team member, and if you're going to be diving there a few days you can just drop the gas at key points in the system and not have to haul it until the final clean up dive. And you'll never use it, so your gas costs are much less than if you actually breathed those stages on every single dive.
Plus, given that Peacock is a shallow system, with a CCR you can do a single 4 hour dive, without carrying a stage, and since you don't have to cover the same boring bits from P1 to where ever it gets interesting, you can spend a lot more time in the interesting bits than you could with two 2 hour OC dives.
Consequently, I am of the opinion that a CCR is a useful tool even in touristy caves at normal 90-100' depths and normal single stage dive penetration distances.
have been seeing pictures of people right after class scootering with a single tank as dilulant / bailout. I am betting if they have a CO2 hit this one tank will not be enough to get them out.
To be fair, I've seem OC divers who were not in my opinion carrying enough bailout gas on their DPV dives either. It was a factor in a fatality at Ginnie a year or so ago.
CCR or OC, however, any pictures are probably not showing the staged gas the team may have placed in the system as additional bailout, so I try not to judge based on a picture or seeing a diver at just one point in the cave.
Most Sidekick divers I know have a long hose for bailout, so it's not just your bailout gas available for the exit, but also the team mate's gas as well. I don't know about you, but in my cave DPV class we practiced gas sharing while scootering out of the cave. The major difference with CCR is needing to manage the loop volume on the "no longer in use" CCR when significant decreases in depth occur during the exit, which might slow the exit a minute or so in total.
You're also possibly proposing a dual failure scenario where not only does the scooter fail, but also the CCR, and in a manner that forces the diver off the loop. I agree you need to plan for a CCR failure that puts you off the loop, but I think also planning for a simultaneous DPV failure is going a bit overboard. At some point you start calculating the risks of driving to the site and you just stay home.
CCRs also offer a couple of options in various failure modes where you can stay on the loop (electronics failures, etc) and that enable you to greatly extend the available gasses on exit.
As for CO2 hits, I've had failures in O2 delivery (plugged orifice), failures on the diluent side (hard to activate ADV due to IP creep in the diluent reg, and a leaking ADV), various sensor failure modes, and floods, and I've intentionally over breathed the loop in OW to see where the limits were at, but, knock on wood, I've never had an issue with scrubber break through.
That's not all luck however, as IMHO, the scrubber is the most controllable and reliable portion of the system with a CCR Sidekick. Use good sorb that has been properly stored, test the mushroom valves prior to every dive, pay very close attention to packing the scrubber (and the axial scrubber on the Sidekick is easy to pack well), don't get cheap and start pushing the scrubber time, and if you've get water in the unit, don't let it sit there. If you do all that a scrubber failure forcing you off the loop is very unlikely. A counter lung failure in a Sidekick is also very unlikely, given how it's made and how it's protected.
Now... that said, I still plan for enough bailout gas per diver to cover 2x our normal RMV over the entire exit from max penetration, and with a 2 person team that ends up being 4x the gas that would normally be needed. If you're thinking about arguing that 4x might not be enough, don't bother. If I have a 45 minute exit from a cave and I can't get my respiration rate below 4x I'm most likely going to die of something other than lack of gas.
