I have had a couple of the UPS units get fried during storms and power outages, but what was plugged in to them has never suffered any damage - they did their job.
A conclusion that works when observation, combined with wild speculation, creates a conclusion.
Start with how electricity works. If a surge is incoming to that UPS, then at the exact same time, that current is also outgoing into attached appliances. Only urban myths claim an electric can be incoming and have no outgoing path.
Second, learn relevant numbers. Electronics will routinely convert a thousands joule surge into low DC voltages that safely power semiconductors. How many joules will destroy a UPS? Always read specification numbers. Hundreds?
A surge too tiny to overwhelm best protection inside electronics also destroyed that tiny hundreds joule UPS.
Grossly undersizing protection inside that UPS means wild speculation (no numbers) recommended the UPS.
If that UPS was doing something useful, they why were so many less robust appliances unharmed? What was protecting a dishwasher, digital clocks, furnace, GFCIs, recharging electronics, LED & CFL bulbs, refrigerator, doorbell, central air, and smoke detectors? Were those on invisible UPSes?
No facts justify that UPS recommendation. If its joule number was any smaller, then it would be zero. Just enough above zero to claim 100% protection - subjectively. Its protection numbers are inferior even to strip protectors. Subjectively: first indication of a scam.
Effective protection always answers this question. Where do
hundreds of thousands of joules harmlessly dissipate? UPS will not even discuss it. Since their target market are naive consumers ... who ignore all numbers.
Hundreds of thousands of joules can only dissipate harmlessly outside. Protection only exists when a surge dissipates outside in earth. Protection only exists when a surge is not anywhere inside.
A 'whole house' protector does that. Effective protection means no damage from any surge - including direct lightning strikes. The numbers?
Lightning is typically 20,000 amps. So a minimal 'whole house' protector is 50,000 amps. Ineffective protectors do no protection - fail. Effective protectors remain functional for many decades after many direct lightning strikes.
That is only protector life expectancy over
many surges and
many years. Protection during
each surge is defined by the only items that dissipates that energy - single point earth ground. A protector is only a connecting device to what requires most attention. To what defines all protection. A 'whole house' protector connects low impedance (ie less than 10 feet) to electrodes that both meet and exceed code requirements. Only then are all appliances (especially a minuscule joule UPS) protected.
Plug-in protectors have no earth ground. And for good reason. They are only Type 3. Must connect more than 30 feet from the main breaker box and earth ground to lessen failure - and fire. Only Type 1 and Type 2 protectors can connect low impedance (ie less than 10 feet) to the other item that does all protection - earthing electrodes.
Nothing new here. Franklin demonstrated this well understood concept over 250 years ago. Earthing surges (including lightning) has been standard over 100 years ago in facilities that cannot have damage.
Effective protection only exists when a protector does not fail. And when
hundreds of thousands of joules dissipate harmlessly outside in earth. Once inside, then nothing will avert a hunt for earth ground destructively via household appliances.
A protector is only as effective as its low impedance connection to and quality of earthing electrodes. Those (and not a protector) require most attention.