The main issues I've seen with offsets is the drastic temp difference from one side to another. That's why I never owned one. Considered it many times, but just couldn't pull the triger on one. I have used them a couple times though, they are quite popular around here, but the temp difference was just too much. I have seen some mods online to help balance temps in one, but looked like something I realy didn't want to dive into.
That being said, alot of folks use that temp variance to their advantage. You could have something goind low and slow on one side and faster smoke on the other.
But whatever you decide, look for something thats heavy guage metal, not just for longevity, but also help hold temps good. Also try to find one that has a lid that overlaps the barrel so that you can control the smoke better. I was never able to find a decent one localy and wasn't comfotable ordering one without checking it out first.
I have toyed with the idea of building my own using a horizontal drum set up with the firebox mounted doen below for even temp distribution. Maybe a project for the future.