If one person in a group buys the game, can't that person play with up to 4 other people that have not paid?
A game like M:tG is priced "per-player". Each player buys their own stuff.
A game like Codex is priced "per-table". One person pays and the whole table can play.
Having bought a set, I'm playing where I can. Forum or otherwise. And yes, TTS's interface isn't very good, but remember it is first and foremost a generic physics engine. Cards/etc are layered on top of that.
People have told me that as a playground for D&D miniatures -- basically a tabletop for people playing "group chat in skype/discord" -- it works wonderfully.