Close to ten years ago I bought a Schiller (Jim Laabs Music) bass trombone with the idea of learning to play it and experiment with it until I understood what I wanted, etc. I was willing to spend the pathetically low cost on it as a kind of throw-away learning experience. Here's what I got and what I've been playing since: https://jimlaabsmusicstore.com/store/sc ... -trombone/ I notice that it's now $100 more than what I paid for it.

I made a couple of ergonomic alterations to it: replaced the silly King-style ring on the slide brace with a French horn hook on the other side of the brace (I have relatively small hands and the hook really helps hold it), and added a Bullet Brace and a counterweight. The only meaningful change was to get the leadpipe pulled, and for some time I used a (drawn) Brass Ark red brass MV50 leadpipe, but recently have switched to a nickel M/K MK 50 pipe.
More recently I've been playing in a big band, and playing a LOT more and a LOT more intensely. I haven't been totally happy with how I've been with some of the double valve notes below the staff (primarily the C and B-natural) in terms of getting them to speak well, especially at brisk tempos. So I began to wonder if I'd finally reached the point where maybe the problem was the instrument and not me.
Today I drove (through dreadful rain) up to the nearest Music & Arts shop to try out possible alternatives. They didn't have much, but they did have a Shires TBQ36YR which I'd identified as a possible replacement for the Schiller pseudo-7B. It's a beautiful instrument. I found it extremely comfortable to hold -- well balanced, and it seemed to have some kind of stock hand brace on it that worked really well, though I don't see anything of that sort in pictures on the web.
It played easily, is more comfortable to hold than the Schiller (even after my ergonomic enhancements), is clearly better made and from better materials than the Schiller, and that low C (and the B) spoke noticeably more easily. But ...
It just didn't sound as good as the Schiller -- not as rich, not the "gravitas" and "bigger sound" I can easily get out of the Schiller. In playing it, it just felt a bit "smaller". Two differences come to mind that might have this effect: (1) The leadpipe. I don't know what was in it, and I couldn't get it out. They didn't seem to have any others in the case. Perhaps a different leadpipe would have made all the difference. (2) The bell. Yellow vs. red brass. But I wouldn't have expected so much difference from the bell. I don't know.
So my final impression was "What a NICE horn! But I can't swap my Schiller for it if I lose a lot of the sound that I have on the Schiller. I guess I'll just work on those double trigger notes a bit harder." This was something of a shock. (I'm also wondering if someone might be able to open up the Schiller valves a bit without ruining them. But that's a story for another day.)