What are we talking about here ?
An interesting topic, as there are more aspects than at first view IMO.
Trying to divide between types:
1. Single small valve only.
2. Small valve for inflating and big valve for deflating.
3. Small valve and big valve, for optional inflating in either of the two (or in two steps - big one first, then topped with the small one for max pressure)
4. Single big valve for inflating (and deflating of course).
I assume these are the ones we most often see, right ?
My thoughts -
1 is obsolete and not used anymore, so not worth discussing.
2 is used by many, and the hassle is with big kites - it takes too long to inflate, otherwise fine.
Especially because you can almost ALWAYS find a kitepump with this "standard" nozzle - even if you forgot your own or it does not work.
3 is excellent, as you can use the big one for the big kites, to pump up easy and fast, and then top it off with the small nozzle.
Downside is, that you has to CHANGE nozzle during the pump-up, which is aaaargh especially if very fine sand in everything.
And for the wavekites (smaller), it does not make sense to waste time changing nozzles at all - you just use the small one.
4 is the "Cab" way right ? I assume it works, since every Cab owner got this.
So they must have solved the issues regarding being difficult to "top off" to the last PSI's, awesome (havent tried one myself as Cab is almost not seen around here - and whenever i borrow another kite, it IS typically pumped beforehand...)
If this issue is solved adequate (assume it is, since noone mentions this as a downside), then I only see two issues -
Is the valve type patented ? Could be a reason why it is not copied.
The other is the risk of standing in perfect conditions, and you forgot your pump (or it is broke), and noone else can help you as a very special nozzle is required.
I've experienced this happen often actually, when we meet at big kite camps - that the nozzle is missing
If I could choose ANY type myself, I think I would like a Cab type (IF it can top up easily), and also another standard "old" tiny valve.
This way, you can get by even if you are stuck without the special nozzle - you might even be able to borrow a toy pump from other beachgoers, instead of having to drive home for the day.