I was in the same boat- couldn't hold sixth gear! Then I got the pipe, but the shop who "jetted" my bike didn't get it right. My first clue is that they didn't change the main jet! All they did was futz with the needle clip position. In sixth my speed would drop (I'd be going 63, then 62, then 59, then have to shift to fifth to pick up speed again!).
I've since taken out the carb and changed the jet from the 102.5 that was in it to a 107.5. Haven't had a chance to try it out yet, but off idle throttle response is a lot crisper. I'm also just learning this stuff, picking it up as I go (carb jetting, that is) so don't take my settings as gospel
I have a future plan of replacing the VM24 with a TM28. I'm waiting on one more part (TM28 cable-choke assembly from LambrettaWorks) and I'll drop it in. Should be fun! Oh, and for the uninitiated, THIS IS NOT AN EASY SWAP!!! I had to have a machine shop fabricate an adapter to allow the TM28 to mate to the rubber flange on the motor side. I used a 32mm Triumph Bonnevile aluminum flange, and had it press-fitted to the TM28.
Back to your question, "how do you like the kit?". It's nice. The connector pipe is stainless, well put together, and the folks at Powroll included everything in the kit including thread locker and the hex tool to change the baffles. It has a good bark to it, a little on the loud side. I think I'm using 5 plates in the Supertrapp. I also believe an IDS2 is a specific muffler, judging by the Google-search I did.
Oh, and for exhausts, overseas are companies that support the MZ. One exhaust brand is "Sebring", but I don't know how to get it cheaply (shipping is a pain!). The MZ dealers overseas seem to have some sort of performance exhaust available, so it might be worth asking. I'll check in with my dealer (SFMoto) and see what they might have available.