I'd wait if you can get them at that price!
If the sumo loach ever sits still, that's when my puff would do it. My bichir would be swimming around and then rest on the bottom for a minute. That's when the pufffer would sneak up and chomp the tail.
But again, mine might have been a fluke. He only bothered 2 of my 4 bichirs, too. I couldn't figure it out. He's been fine with every other fish. :/