I know the best kind are the ones which would be wired into the system, but saw this today and wondered if it would be any good. Is this a "better than nothing" or "you get what you pay for" situation...
MOVs in surge devices degrade over time. If you have a catastrophic failure in a MOV you could be looking at a fire issue. Most of the better surge devices have a built in circuit to indicate MOV failure. True surge suppressors should be replaced after a period of time because of the MOV degradation. Regardless of which one you get make sure it is UL listed to guaranty it will do the job.