It´s pretty unlikely that they kill tanks, yes, but they are hard to spot and they force the tanks to remain buttoned, so your ATG is less likely to be detected or your assaulting infantry has a better chance to succeed.
Besides that there is a low chance that the target may become immobile or recieves a gun damage.
So, if you have some ATR, use them. But I wouldn´t waste any points on buying them.