I have regular old APC UPS's on my PCs and they work fine. The PCs handle the switching glitch OK. If he keeps fresh batteries in the UPS (replace about every 3 years) he will be able to count on about 80% of the rated capacity. That should give a reasonable reliability if the system is attended but it sounds like a one man band operation so a power cut at 3 AM may bring him down if he doesn't wake up, start the genny and flip the transfer switch.
