Just because it's made by nVidia doesn't change the fact it's still integrated graphics with shared memory.
I agree that you should get revision B at least. I don't argue the fact that there have been some people who are/were happy with rev. A, but too many units suffered common problems (overheating etc.) to take the risk IMO. Take into account that people who have issues with the computer are more likely to sell it than those who got the perfect one, and it isn't really like they're selling a faulty unit, because Apple's official policy is that it's normal. So even if it's someone you know they may simply not know theirs is a bad one and tell you everything's alright with it - and it's hard to check.
Also note that even though specs seem similar, almost every part was upgraded between revisions A and B - CPU (Merom -> Penryn), RAM (DDR2 -> DDR3), drive interface (PATA -> SATA II), drive storage (80/64GB -> 120/128GB), GPU (Intel -> nVidia). Revision C only got new battery, slightly improved CPU (within the same architecture) and less underclocked GPU.
On the other hand, main issue with revisions B/C is "grey lines", which have been discussed to no end already. This is easy to avoid if buying used though, because you can check for it immediately.
Then there's a matter of HDD/SSD. I get it that it's a secondary computer and you probably don't need an SSD, but if you're considering revision C/HDD, keep in ming B/SSD is $50 *less* and will feel faster in everyday use.