Fun, and useful, although a bit "long in the tooth". Some of the more recent (well, later) test records, esp. some of the Japanese-made ones, will do more sophisticated things, and were produced with a higher degree of precision, but the Command LP is quite okay to start with. Use it to get what improvements you can from it. Then when you get an even better one, you can make further refinements to your set-up.
Command records were among the best made for their time, and aren't bad, but they come from before the technology had really hit its peak. Also, because of their age, there may be some real wear on the disc, affecting its sound.