Update on the X88 I recently purchased:
It was manufactured in 2000. It reminds me of something from the 80s, though. The buttons and general operation can be a bit obnoxious, especially having to move the test leads around constantly for the different functions.
I went through the full calibration procedure and adjusted everything, about 20 different potentiometers, half for the input, half for the output.
For the input, it's essentially a 15,000 count DMM, but has very limited capabilities compared to a typical DMM, both in functions and ranges. Input protection is nearly non-existent.
Compared to the PDVS2mini, the DCV output is nothing special, of course. What you set on the display is what you get, but the "imaginary" digit past that is a little bit jumpy. Same goes for the 100mA DC output. Strangely, you can't actually select 100mA, only 99.99mA. This variable DC constant current output is probably the main thing I can see using this for at the moment, as it's more stable/precise than any of the bench power supplies I have.
The 'interesting' feature I like on this is the extensive RTD/Thermocouple simulation capabilities (it can read via the inputs as well). You can pick a specific temperature in C/F and simulate this to a DMM. So for example, I can choose K-type thermocouple, set the output to 900F and connect it to a typical DMM and bam, 900F on the DMM. Fun.
It also can do some 4-20mA loop functions, but I don't have any use for that at the moment. The previous owner was an HVAC tech, so they probably did use that.
So ultimately a cute/interesting relic, but how useful it is to you will depend on your situation.