I agree. Tiger barbs are fin nippers, and as you say they will even take on fish many times their size. They are particularly bad with fish that have long flowing fins such as bettas, fancy guppies, and angle fish among others.
You might get lucky and get some peacful ones, but I wouldn't count it. Its too bad, there are a very hardy fish that are colorful and fun to watch. I have had them in a tank with other fish before, but only with fish that were fast swimming and had realitively short fins.
When I had them, I too only had plastic plants, but I can't recall reading anywhere that they will damage plants.