Me and my friends have both a single and double hose hookah. Most of the time we block the second hole one the 2 pipe hookah anyway, except if we are a lot. We usually just jam a apple on the pipe tip HAHA
I would say rather go for a single pipe with a smoke release valve.
We have modified our single pipe to be able to use 2 pipes, just screw of the tip of the smoke release valve and press a second pipe on their, and then tape. Works great for us.
Another thing that is worth considering when buying a hookah, is size. Too small seems to be stronger to me (which I don't like) and to big is inconvenient. I think a medium size (about 15") hookah is just right.
Good luck and enjoy the new KM!