Iv'e dealt with my fair share of neotec 500 series monitors, and it's older brother 2500/2700 series. They are not without problems, but they are simple enough to fix, and parts used are common enough to still be available.
biggest issue is the caps. Keep an eye on them and replace them before they fail and it will serve you good.
occasionally you have a blown HOT transistor, but the design of the neotec is smart enough to shut down the power supply to prevent further damage.... can't say the same thing about wellsgardner monitors.

the tubes used can be problematic, sometimes there is significant burn-in on a tube that is only maybe 2 years old (mind you that's 24-7 use.) while others didn't seem to have that issue.

overall i would rate the reliability of neotec monitors an 8/10 and for "shids and giggles" the wellsgardner 9000 series digital monitors 5/10.