We've got one at work and it's great when you've got a lot of hard drives coming through. I don't know if it's a great idea to use long term on the same drives over and over again, as it may place stress on the connectors (it doesn't seem to, but it could be happening). I've also heard that sata connectors aren't rated for that many connects/disconnects, but that seems like an unlikely failure mode that I've never heard of actually being a problem in practice.

If you're backing up in a store it and forget it process like picture backups, it's a great convenience. If you're going to cycle through the same three drives, I'd bite the bullet and buy proper enclosures.

Matthew