I love my Klose for catering. The dog and pony show is something customers really do like. It alone will not get you jobs, but it does add to the ambiance of a party in a way that standing around a cabinet does not. I did a party last year where they took a section of fence out so my Klose could be placed in the backyard. I think another brethren caterer has had the same request. As Phil says in another thread, it's the "BBQ Show"...
That said, I think you need both. I am buying a Backwoods to mount on my Klose. There are too many times(like always) that you need the flexibility of multiple temp zones that no one cooker can provide. Also, the more you cater, the more you are going to need a set it and forget it type cooker. there are just times it is not a good use of time and energy dicking with your stick burner...
I don't think it probably matters which one you start out with...
Klose 72" Mobile
22" Weber Kettle(10 bucks@garage sale)