Indeed probably not too much.
4-HO-MET is a 5HT agonist like psilocin while MDMA is among other things a 5HT and DA releaser, a 5HT reuptake inhibitor and also part of its mechanism has to do with 5HT agonism - I think MDMA is sometimes described as an indirect 5HT agonist but not a direct one.
That means that there is a slight similarity but not all too comparable, furthermore the moa of MDMA is fairly complex and not well understood while 4-HO-MET is not even researched that much (although its quite likely not very different from psilocin).