I play tenor and bass trombone (keen amateur) but was curious about alto trombone so I decided to get the TEB480L.
In general the instrument is very good, sound is nice and it speaks easy. Intonation is good, the partials are well aligned. Slide out of the box was a little rough but after playing for a while and a couple of cleanings later has turned out to be good.
There are some (very) minor cosmetic blemishes in the lacquer, but totally in line with what to expect from a instrument at this price point.
Overall I am very happy with this instrument, it allows me to learn alto and is would be more than sufficient for the occasional performance.