I've never used the mobile clinics, but I know in some areas they are very popular. One thing I would check is what type of anesthesia protocol they follow.
http://www.yorkietalk.com/forums/yor...-protocol.html
Some other things to investigate:
Do they do pre-op blood work?
What arrangements do they have if your dog needs extra help/care while coming out of anesthesia? (Do they have a vet clinic close by?)
How about pain medications and follow up care?