I would say they're "legit," after all the link is a reputable brand (Square-D) and the engineering of surge protection isn't exotic. But you have to remember that surge protection in all forms is a bit of a statistical gamble. Surges come in different forms with different peak voltages, different pulse widths, some are oscillations, some are more DC pulses, some are due to equipment on the power grid itself, (a substation dropping a big branch line can put a surge on the lines that aren't dropped, for example), and some are external like lightning strikes. A protector can only do so much, it can't really guarantee that no abnormal voltage pattern get through... it just decreases the odds of damage. And many surge protection devices do so by taking on damage themselves, so they have to be replaced after doing their job.
What I've chosen to do is put individual smaller surge protectors on my devices that are either high value or high sensitivity... things like the main computer, the TV, the expensive fridge with an electronic brain and variable-frequency drive compressor, etc. In other words, I let the lower-value stuff on my home power grid (old style more rugged motors, light bulbs, resistive loads etc.) take some of the brunt of surges and let the point-of-use protectors "clean up" whatever is left over right at the device to be protected.