Programmers that are no longer made are still viable programmers but may be more difficult to find. eBay, Craigslist, and other similar sites are good for finding these models.
The Data I/O Series 22 is very old but will program VERY odd chips such as the tri-voltage TMS2716 EPROMs and other EPROMs that most other programmers will not touch. It will NOT do negative voltage chips such as 74S186 PROMs or the ancient 1702A EPROMs.
The Genius G540 is still getting software updates regularly, so compatibility may improve over time. It does not have an optional external PSU. The software has support for TTL testing however in practice this function does not work.
Programmers with 40 or less pins are not appropriate for MVS and CPS2 conversions.