Hell yeah, a GBB thread i can actually provide quality info on.
I've always used a TM M9 as my sidearm and let me tell you, the extra $35 is WORTH IT. I've owned two of their Tac Master M9s and always ran them on propane. The first one i bought from Eagle back in 2011. It was very used, i'm thinking it was at least a few years old at that point. Part of the slide did break off during firing once, but it didn't affect the function at all. I'm thinking that i might have hit the slide or something which caused it to crack in that area. I used that M9 from then all the way up until early last summer when i bought a new one to replace it, and man, that thing is a baller. It's stock range and accuracy is consistent with friends' upgraded Glocks that i've compared it to. That extra $35 is really saving you money if you planned on doing performance upgrades. You are also going to get that TM build quality that really is as good as everyone raves it to be.
Will you need to replace the slide? I wouldn't count on it. It's just the experience i had, but my first TM was used by me for 7ish years, and the only damage it suffered didn't even affect the performance. Just don't go installing harder recoil springs or using CO2 down the road lol.
One tip that i find pretty beneficial: Don't add silicone to your propane. If you are good at working with your hands, break the gun down and lubricate the appropriate parts with a quality grease. When you add silicone to the propane, the silicone travels where ever the propane travels, meaning your hop up that requires friction to work properly is going to start getting oily and lose its effectiveness. Your barrel will also start to get oily which promotes the collection of dirt and dust inside it.