I can't comment on the difference
because I haven't ridden a Voyager without the KAMS.
I can tell you that MY 2012 Voyager with the KAMS was about as hot on my legs as my 900 in summer temps.
That means it gets a little hot. Waiting for a long red light or heaven forbid a train, will be VERY unpleasant in summer temps.
Even at slow speeds you can move you foot to the side of the board and the wind will keep your leg reasonably comfortable.
The 'hair dryer' keeps the jewels from burning up and the wife says that it doesn't dump hot air on her either.
When I installed my pipes 2 weeks ago, I wrapped my headers with 15' of exhaust wrap and riding in the 80s I don't feel ANY heat.
As you know; SOME of these bikes DO run hot beyond just our perception.
Mine, ran just past the last white mark and had a warm engine 'tic' until about 2k miles.
Changing to synthetic stopped the 'tic'; I have flushed the coolant and use a 70/30 mix and installed tri-ovals & a PCV.
So, far my gauge hasn't read past the 'fan-on' position this year.
All things being equal, the KAMS is nice. Re-starting your odo and warranty will be nice too.
I think it would be a hard decision.