One a slide and the other a valve. I played the slide one throughout middle and high school, but there is an interesting story on how I got the valve trombone.
You see, the summer before my sophomore year of high school, I decided to do some bike tricks. Needless to say, and I still clearly remember it to this day, I did not properly land the bunny hop off of the handicap ramp. I actually shattered the back of my right shoulder. What makes the situation even funnier/worst is that, again, I play trombone and marching season would be starting soon.
I actually marched a few shows without a instrument while in a sling. Sometimes I got bored and sang the tunes. Anyways, once I mostly recovered, my parents bought this valved trombone for me to play and march with. I didn’t play it for more than a few months, and I picked up the slide trombone once I fully recovered.
This happened 14+ years ago. My parents have been trying to sell the valved trombone this whole time, and either no one is interested or they look down upon it (“true trombones are slide, *rabble rabble rabble*). Recently I’ve been wanting to play any/all instrument I can get my hands on; so I bugged my parents to ship the valved trombone to me. They finally gave in.
The valve trombone is a piston valve; there is also a rotary style and a Vienna valved style that exists. It’s in the key of Bb, like it’s slide counterpart. I’m told it has the same fingerings as a Bb Trumpet. The logic is the same though, each valve increases the length of tubing, so the 7 positions of a trombone slide are in fact all there (I checked).
The biggest difference is that you don’t need to tongue the notes as you do with a slide. And you can’t do a true glissandos (sliding/slurring one note to the next, the specialty of the trombone). Back when I marched with it, it was like a new instrument that sounded very familiar.
Also, word of advice, these things are heavy with a lyre on it. Would not recommend marching with it.