Interesting? Depending on your priorities, that may be a bit of an understatement. From a performance perspective, even more interesting might be the addition of a motor with twice the power of the OEM? I'll leave that to your imagination....
Regarding battery usage difference, OEM vs. Bolton's kit, there is little doubt it's possible to decrease your range. The kit works as it's allowing more power to the motor at higher power settings. The bigger point that's not mentioned, is the fact that similar power settings (OEM vs. kit), there will be NO difference in battery range. Because it can pass more power to the motor, does not mean it will be doing that full time. The only time it's is supplying more power, is when YOU are telling it to.
You ARE able to limit the available power to the motor using the available parameter settings - easily. Same if you want to assign a upper speed limit.
There will be no more of the OEM "soft start" either. The bike will go when you tell it to, from a stop, or when asked to accelerate when already moving.
I can't speak on the water resistance other than the fact our bikes have made it through quite a bit of travel time while being towed in an open utility trailer with pouring down rain.
And last, the PAS firmware is VERY well done. You hear/read about bikes that won't go under 10 mph in PAS 1, and so many other PAS issues, this controller is very nicely done. As good or better than most others.