The difference between cheap and quality is that the quality unit in this case DOES NOT RELY EXCLUSIVELY ON MOV's for protection! It utilizes a combination of MOV's and capacitors amongst other things, which not only means that it will NOT immediately start degrading the second you plug it in, but also that it CAN and DOES result in increased voltage stability. I have them in use at my house, where at the outlet voltages would swing +/- 7 volts without and with the ISOBar the swing is +/- 1.1v (that's the absolute highest I've EVER measured.... it's typically less than half that). I also put them into my mother's house when I built her home theater, resulting in voltage swings going from +/- 10.5v to a hair over 1v.
For someone who has a LOT of very sensitive, very expensive audio equipment (amongst other electronics), there is a MEASURABLE increase in SNR, and a drop in distortion when the same equipment is running off a high end unit like the Tripplite vs a cheap $15 unit (as measured with some very high end equipment, which is used to ensure that the audio output is always identical, necessary in a recording environment).
Sure, if you are protecting against FATAL surges like a lightning strike to your residence, nothing short of a whole-house grounded protector will save your stuff. I have two whole-house protectors installed for peace of mind.
In my last house, however, with NO whole-house surge protectors, the transformer box IN THE FRONT YARD suffered a direct lightning strike, and I lost exactly ZERO equipment hooked up to the ISOBar's. Of the 11 in use, only 3 units were even destroyed, but they did their job admirably. And if you have a high-magnitude surge, YOU WILL BE GLAD you sprung for the QUALITY unit encased in a powder-coated high-grade steel housing rather than a plastic unit (they melt, I've seen it countless times...).