I have DZ-1000 machines on most of my switches and I still have a few NJI machines. The only problems I have had with the DZ-1000 machines were caused by the way I use (or misuse) them. The NJI machines use more power than the DZ-1000s so if I have a DZ-1000 and an NJI wired in parallel (for a passing siding), the DZ-1000 doesn’t always work. Exceeding the DZ-1000 voltage rating can cause them to come apart, but that can generally be repaired.
I don’t have any DZ-2500 machines, but from what I read, they are slower speed and easier to set up for remote (TMCC/DCS) operation.