There's no such thing as a Gen2 G27. They all look the same, with the 3rd gen finger grooves and no rail. They are too small to have a rail, and that's true of the Gen4 as well.
I would never hesitate to buy a used Glock. Thoroughly inspect it to make sure nothing is broken. Check the serial number against the recalls. You can even send it in or if you're local take it in to the factory to have them inspect it and do any internal parts upgrades that it may need. You would probably have to pay for shipping, but they would do the upgrades for free. They will also, if you wanted, refinish it for (last I heard) $65 and you can have it looking like new.
Depending on how many rounds have been through it, it might need a recoil spring, but those aren't expensive. Same with the mag springs. They could be fine or they could be a little weak, but even if they're a little weak, they usually function fine.
Odds are, it will be perfectly fine and will function as well as a new one. That said, there have been minor design changes with both the internals and the magazines. In a gun of that age, the magazines will not be able to be updated past the #5 follower, where the new ones (again, last I checked) are on the #8 follower, because of internal changes in the magazine. I had no problem with any of my magazines over the years, regardless of what follower was in them, but I do like to keep everything up to date.
My Glock 23 was built in 9/90 and my 27 was built in 9/99. The 23 needed updates, the 27 didn't, but it already had the updated recoil spring assembly. I never had problems with either one, but I still took them in for inspection and upgrade at the factory anyway. My 23 functioned fine before the parts upgrade, but it was called for, so I had it done.
If you're happy with looks, function and price, then go for it.
