The one enormous flaw that I found is what to do AFTER you use it. The manufacturer recommends tethering it to the back deck. The problem with this is the dragging float strongly pulls the kayak to that side, making forward paddling very difficult (I do not have a rudder). Worse yet, trying to find and then use this tethered float if one re-capsizes is quite difficult. The system I came up with that appears to solve these problems is to attach a small circle of bungee cord to the handle, then slide this bungee loop onto your arm. You're then wearing the float on your arm. It is easy to paddle like this (although the wind can certainly get high enough to cause problems), and it is very easy to simply slip your hand back down to the D-ring handle and re-use it if you have another capsize.
I believe this is an enormous and important safety addition to the safety repertoire of any kayaker in any but the most benign of conditions.
I always believe in having a backup or a plan B. In rough water especially cold water I want to know that if my roll fails I have another option before deciding to do a wet exit. Which could be fatal.
This has nothing to do with how good my eskimo roll is. I want to know that I have a second option. The BackUP is just that. It automatically inflates and gives you something to hold onto to right yourself back up in a matter of seconds.
Its a must for someone who isn't as perfected on rolling. Once inflated the float also serves nicely as a paddle float. The only downside is that you have to replace the CO2 cartridge each time it is used.