If I was reviewing Thomann TR 25G B-Pocket Trumpet, I would give this instrument a solid 4 stars.
I ordered this instrument twice. Both times, it had a lovely warm tone and a great response; somewhat like a cornet but sweeter. It probably lacks the projection of a full trumpet, but the response felt as good as my main trumpet (B&S Challenger 2/S) which is saying something!
For the first instrument, the downside was major intonation and tuning issues. I played it in the local community orchestra and no matter how I tuned it, some notes were always out. Slurring between E and G at the top of the stave, they were simply not in tune to each other.
I got a refund and reordered it, and the intonation for the second instrument was a lot better... if it wasn't for being a semitone too sharp. With the tuning slide in the normal position of about 1/3" the instrument was still a semitone sharp. Sadly when I pulled out the tuning slide about 1.5" to tune middle G to my other trumpet, that negatively affected the intonation of all the other notes so it was not a viable option.
Sadly I will be returning this instrument as well in favour of the Carol brass pocket trumpet (which by all accounts is a great instrument).
If you are seeking a trumpet in the key of B, I would recommend it; alternatively if you are playing by yourself and don't care what key it is in, you could take a punt. My opinion is that with the whole instrument being a semitone sharp, there are key problems with the design so I would avoid it.
I have had a great customer experience with Thomann though, free return from the UK! They did not win their awards for nothing.