Is there a demo or a free trial?

Yes, a free account. Sign up at rangeconverter.com/users/sign_up and verify your email. Your lobby then has a Free tab with preflop sims across several games, in both the GTO Trainer and the Range Viewer. No card needed.

Reg and Pro are sold per game and add more sims and tools. Open any game in the Lobby to see its sims and what each plan includes.