There are two types of these "hobbiest" DTS CDs.
Type One are created from 1970's vintage Quadraphonic tapes and LPs. These are generally discrete mixes of music released in the '70s. However, the results are dependant on the source material, the electronics used to decode and/or record the sources, the hardware and software used by the converter, and the skill of the converter with regards to recording, processing (NR/EQ, etc), and final creation. There are many that are good, as well as some that are not. In fact, many of the popular titles have been done by many converters, so you may have to search a few times to get one that's good.
The second type of hobbiest DTS CD are those that have been sourced from stereo sources, then "futzed" with using software and hardware phase decoders. The results from this process vary widely. There are some that have created excellent results, such as the "TOUP" discs. Again, others are so-so.
Whenever you are dealing with these "hobbiest" titles, it's pretty much a crap shoot.
However, if the labels released this stuff properly, and with regularity, all of the above would be moot.