I don't have much to add regarding the SMS 75, other than the KISS Sidewinder CCR was designed to be used with the SMS 75 - it works with other BCs, some with and others without some mods, but it was designed around the SMS 75.
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In general, side mount rigs break down into two categories:
A) rigs intended for use in deeper caves with steel tanks (such as north Florida cave diving where the depths are deeper on average); and
B) rigs intended for use in shallower caves with aluminum tanks (such as in Mexico).
Side mount cave diving also breaks down into two categories:
1) diving in caves using a side mount configuration; and
2) actual side mount diving in a cave that requires a side mount configuration.
For number 1 above, the "A" category rigs will work just fine. They have excessive lift and bulk in some circumstances and may be less efficient, but they'll have enough lift and most can be made to trim ok with aluminum tanks. For number 2 above, you need to be more selective. For example, 25 pounds of lift won't be enough for large steel tanks a couple stages and a deco bottle, even in a dry suit. At the other extreme a Nomad XT with it's 60 pound wing, tail plate and fair amount of bulk will be a lot less than ideal for a shallow in tight passage with a pair of AL 80s.
There are some rigs in the 35-45 pound lift range with tail plates that can manage both ok, but they'll be biased one direction or the other based on lift capacity and presence or absence of a tail plate and towel bars.
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It helps to know what you really want, and you'll have a better idea what you really want if you can work with an experienced side mount diver. I'm strongly biased here as I've seen some truly horrible open water side mount divers and configurations, so I'm really suggesting you find an experienced side mount cave diver as a mentor. The same caveat applies to side mount instructors. There are truly horrible side mount instructors out there, and don't be fooled by their instructor card. For example, one particular agency will allow an instructor to cross over to becoming a side mount instructor after just two dives in side mount configuration with an IT. Thus it's possible for a side mount instructor to have less than a half dozen total dives in side mount - with all of that in a single side mount rig with a single class of tanks. Don't expect a font of knowledge, experience or wisdom to ensue from that process.
A mentor also offers some significant advantages over an instructor. They can be easier to find, and it can often be a longer term relationship with some on going support and coaching over a much larger number of dives. Either way, a (qualified and experienced) instructor or mentor will take a lot of the slope out of the learning curve and get you squared away in a minimum number of dives. I've had divers ready for a cavern and intro to cave class in as little as a half dozen dives (but that's more the exception than the rule).