Did it say what kind of rootstock is on that tree? If it's a dwarf tree I would definitely pass. You would really have to water it heavily to get it through this first year with all those leaves and fruit. That's a really big tree relative to that root size, so I would be concerned about that. I would probably pass on them unless they had a great sale that was worth the risk.
Having said that, I occasionally buy potted trees like that if there is a good sale and I'm in the mood to plant another tree. If you can water them heavily the first year they will probably live and after that you are generally in good shape.