I'm going to go against the grain, here, and point out that you have a simulator that's probably as good as that Slow Stick, for the purpose of getting prepared for the LT-40. Furthermore, the sim will be useful later, when you've mastered landing with the LT-40, and want to try loops, rolls, etc. You can practice on the sim, and you'll find many things similar.

The Slow Stick would be a good experience, I believe, but completely separate from that you get from the simulator and the LT-40.

It's your money, and I wouldn't say anything bad about the Slow Stick, but my opinion is that your time would be better spent on the sim.

Hey, welcome aboard!
Dave Olson