Well, having owned and used one of these for two years of which I've only gotten about 20 dives out of it as it didn't work. The first I couldn't turn it on with the remote, second the batteries died after 3 dives. Right now it seems to be working. Out of a big group of divers I know here, there maybe two that haven't had issues with the vest.
I know of one diver here whom got a pretty bad burn on her back from it, blister/etc from faulty wires in the vest. How do I know this was for sure, well I was in a relationship with her at the time and saw the blistered burn.
Another friends basically melted while being charged. Thankfully he wasn't wearing it. Turns out the wires shorted in the vest. This is one of my good friends.
Most issues have been batteries not working or charging. This is quite common. This was pretty much everyone I know with one of these
Granted, all were taken care of by the distributor/manufacture and usually there is lots of issues with newish type products
With regards to heat, the heat from the suit is on the back of the vest. They use some sort of wiring that gives of a far infrared heat? Think that's the name, anyways the wiring used is quite large and pronounced, putting it on the front of the vest will result in pushing the wires into your skin from the drysuit compressing. This can facilitate getting a Burn. So to compensate for this they put it on the back so it is not being compressed. Sadly with the heating pad being in the back I tend to not be as warm and my chest/kidneys get cold.
What I do is flip it around to the front and only use it if I get chilled. Otherwise I risk getting a burn. I've warn it on for two hours and I had red marks in my chest from the battery for hours on low heat and turning it off and on . I still wear it this way as the heat in the front is a lot nicer and keeps me warmer on deco if I need it., I just tend to wear a thicker undershirt now to give me a bit more protection.
Now would I buy another one of these?
Nope, the only reason I did was it got the gf and me into one for less then the price of a santi system and battery pack. If I only bought one I'd have never seen it as we all know. It would have mysteriously made its way into the her basket under its own power obviously
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The reasons to choose an external battery over the thermulation system are as follows:
1. if there is an issue with the batteries/not being able to shut the power off to the system can result in some serious burns. With a external
Pack you just unplug, the thermalutions your screwed. I've had a remote that wouldn't communicate with my vest to turn it off our on, that was a very hot dive when I got the best in but it wouldn't turn off.
2. If the batteries begin to short out/etc one can easily jettison and external battery supply off their person underwater, try doing that with the batteries in your drysuit. Granted the batteries are sealed and meant to be submerged but that doesn't guarantee anything these days as qc with a lot of companies is horrible.
3. There have been way to many issues with these vests. Even from the new generations. I know a lot of people whom have these none are overly happy with them. I know a few dealers outside of my area that refuse to sell the yellow grade vests due to all the issues and returns.
4. The remote is depth limited to 300 feet. Or was that 200? Anyone doing serious dives or dives deeper then this when your going to likely incur more then 15-20mjns of deco has lost the ability to turn the vest on, thereby making the vest useless. What's that you say, clip it off on the up line? Sure but what if I can't make it back to the up line.
5. Inability to plug the heated vest into an off board source, scooter, extra battery pack, etc. many use the scooter or battery packs from camera lights to power these vests.
The thermulation vests provide good heat and are a great starting point to get into heated gear. That being said, they are an entry to low-mid level product that covers a certain area of diving. Keep in mind these were/are designed for wetsuit diving. They have been adopted for drysuits, which is not their intended use.
The santi or other systems mitigate/relieve a lot of the issues I mentioned above and with tech diving one has to be able to handle issues under the water., we cannot just go to the surface as we may have long decompression obligations. That being said those vests have their own issues and I know people whom have been burnt by them as well. Also they don't allow one to control the heat level without putting in more controls/wiring (drawing a blank on the name). The heating elements in the others seem to be a lot less prone to digging into the skin(tape/fabric) when worn with the heating elements on the front, and they provide the heating in the vital areas (chest and kidneys). That alone is a major selling point.
One thing to keep in mind Is if planning your dives around heated gear, stop and rethink what your doing. I'd suggest buying better undergarments prior to buying heated gear. The heated gear should only be used to augment your diving not keep you warm in the entire dive. Most of use just use it during deco to help with the off gassing. If your using heated gear in temperatures above 50f or 12c, you really need to look at better undergarments and more layers.
That's my two cents on it and I'm busy putting together a system here for the winter months and colder/longer dives.
Whatever you choose to do, make sure you look at the pros and cons for both and chose what will suit your needs as a diver and budget. Either option will provide you with heat, however they are completely systems., meant for completely different diving.
Happy dives!
Regards
Steve