Incredible value for money
I've now been playing this horn for a couple of months and I am incredibly impressed by it. I play for a brass band and before this I played on a Bach 50BG which was briefly followed by a King 6B. The Thomann proBONE 3 simply outclasses both of them.
The proBONE 3 plays like a far more expensive instrument, very responsive from sailing around above the stave to the depths of the pedal register. There isn't a register where it becomes cloudy like I had experienced on my previous instruments.
The tonal quality is very good, giving a deep sonorous sound in the quieter parts and the classic bass trombone 'rip' when things get louder. The tone is far superior to the Bach I played on, which was quite thin. The King gave a similar sound but was far less forgiving if you slightly miss-pitched.
The valves are currently the best I've played on. Incredibly smooth action and just the right amount of resistance. They do require regular maintenance (I oil them once a month to keep them in good shape), but this is not much difference to any trombone. I have found that after an extended playing session, engaging both valves can become difficult. This (for me) is down to the horn resting on the hand-thumb joint when both valves are engaged. However, this happens so infrequently I don't even count it as a con.
The only slight downside is the slide. It isn't the smoothest ever. Again it is better than the Bach, but I consider the King superior in this respect. This isn't to say that it is a bad slide as it is far from that, but it could be a little better.
Apart from the instrument you also get a Pro-Tec case (which aren't cheap!) and a full cleaning/maintenance kit, which whilst not expensive by themselves is a nice touch. It is essentially an all-in-one bass trombone kit.
Overall, an incredible horn for the money and I would recommend it to anyone who doesn't want to spend ~£5000 on an instrument.