The classical trombone is very much alike the Barock-trombone.
The biggest difference is the slightly wider bell-flare. These instruments are mostly made out of copies of a instrument in Nürnberg Stadtmuseum.
A trombone builder called Eschenbach made these models - here rebuild by Geert Jan van der Heide, in Holland.

These instruments are very nice to play Classical works on, such as Mozart-Masses, even as late as Schubert Music.
I have played Schubert Symphonies on these trombones, and it certainly gives the trombone-section a special sound.
Afterwards, I am not really happy with the balance of the group, and I believe that we would do it different today. Since it takes quite a while to get a proper grip on the qualities of the instrument, it was a bit hasty to do recordings at such an early stage.

It is still a bit problematic to find the proper mouthpieces - especially that fits the whole section! - and that makes a homogene sound with these small trombones.
Often, first-timers react negative towards the thin, bright and harsh tone. Especially the alto-trombone can be very daring to play.
It sometimes needs to be treated as a 3rd trumpet, especially in Beethovens creations, and will sound very brutal. but if the section knows how to handle this and back-up the alto, then a very fine Brass-sound can be achieved. Sometimes Full, and sober - sometimes Hard and nasty. - without covering the rest of the orchestra -