Personally, the only way I would buy a 5-volt PS2 is if the price were substantially more than $200 (price of an upgrade kit) less than I could get a 3-volt PS2 for. I believe I've had 6-7 5-volters. After 3-4 had failed, I upgraded the rest and sold off the 5-volt boards that hadn't failed.
If you do buy it, check the battery. If it's white remove it and replace it with a new battery.