It seems to me after reading an awful lot about the various H&N systems that while they may all be very helpful in a crash the real determining factors for me are these:
1. Which ones provide the most latitude to install incorrectly?
2. Which ones are the hardest to get out of the car in an emergency situation?
3. Which ones restrict normal head movement when driving?
4. Which ones affect a persons seating position (seat set up, etc.)?
For me, and this is just me, I have paid quite a bit of attention to my seat position angle shoulder strap heights, etc. to fit my body which has a very long torso creating different issues in seating properly and in comfort. As I look at the various solutions offered by the various manufacturers of H&N systems I see draw backs to each for my particular situation.
What I think is important for each person to decide is not what is most popular, but which one works for your set up and provides safety. Only the individual can decide which one works best for their situation and deciding safety is limited to the published data for each device. So I come back to my questions and here is how I have answered them for my situation:
*Assumption: I have ruled out all but the Hans and Isaac devices because the others seem to have more issues, at least for me in the overall assessment.
1: It seems to me the Hans has the most latitude to install incorrectly or allows the user of the device to allow the device to loosen up the straps over time. This is the critical factor in saving your life. If those straps are too loose then your head will incur a big load once your body begins to stop in an accident. On the other hand the Isaac does not suffer from this situation since the shock does not allow "slack" to occur. There are also the issues of slippage on a Hans that many seem to complain about. I am worried for in my case that having such a large device on large torso will just aggravate by seating situation.
2: I think both the devices suffer here in that the Hans makes it difficult to get out of the car window if needed but is easy to get out of in you are awake and alert. The Isaac you must be awake to unbolt the latches on the helmet but then it is easy to get out of a window if need be. For me, as a big guy, having something large on an already large body is not appealing.
3. This is a tough call because in the case of the Hans it depends upon how tight the straps are while the Isaac it does not matter. I have talked with people about this and they have loosened the Hans straps to gain mobility. For Isaac users they seem to only notice a slight restriction when in the pits but do not notice it on the track. Again, loose straps make the device less effective.
4. It appears after trying out a Hans that my seating position is somewhat changed, or at least feels like it is changes and is less comfortable, in my opinion. This might change over time, but I like my seating position now as it is very comfortable. The Isaac, which I have not tried yet, seems like there is not affect to the seating position what so ever and works well with your seating position.
So those are my thoughts in my case. I welcome other thoughts regarding my situation that I may not have thought about, note I have not put all my thoughts down just what I have boiled this whole thing down to be for me.
Let the debate begin (Greg, Craig, you are welcome to chime in here as well, but let's keep the debate on the technical merits of the points

)