Uh oh, just did a check and I am mistaken. They stamp the AR on the housing. I have no idea how you find out the trim unless you bought it that way. Will let you know if I find out.
Trim refers to the relationship between inducer of the compressor wheel against the exducer of the turbine wheel.
You can read more here:
http://www.turbobygarrett.com/turbobygarrett/tech_center/turbo_tech102.html
Your life would be easier if you had a Garrett turbo coz you can calculate the trim from the 4 digits.
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400, 460 and 490hp depending on the trim - 54mm, 57mm and 60mm respectively.
As for whether it is a good turbo, it really depends on your application. If you stick a big turbo on a small engine and get no boost, will you say that the turbo is bad?