Is my surge protector really a surge protector?
Can the supplier give you a specification sheet showing what it protects against and what the component technology is inside of it? There are industry standards for Surge Protective Devices, (SPDs) administered by UL under standard number 1449 that separates them into different usage categories (hard wired, plug in, large, small etc. etc. If this thing is not UL 1449 listed, it is likely junk. If it is, then you would need to know which class it was and compare that to how you are using it.

https://www.ul.com/offerings/surge-protective-device-testing-and-certification-services

This UL site can direct you to a database they maintain on all of the different manufacturers and suppliers by plugging in the data you have on it and seeing if it is there.

Even if it is listed, that doesn't mean it is good, it basically just means it was tested to some minimum standard and will not start a fire (which is really what UL is about anyway). But the general rule is that the cheaper it is, the less likely it is to be of any real value. Most cheap SPDs are just what's called an MOV (Metal Oxide Varistor), a device that only conducts when the voltage rises above a certain threshold. 

So what happens is that a "spike" of voltage comes in from the utility line, it exceeds the threshold of the MOV and the MOV conducts to ground, protecting your downstream equipment. That does work, except that when it works, the MOV is often sacrificed in the task, meaning it only works once or maybe a few times (if the spikes are low), then it is vaporized and no longer there. But you can't tell from the outside, so you don't know. So in my opinion if you are going to buy one at all, buy one with some sort of indicator, usually an LED, that tells you when it has done it's job and is gone. That way you at least know you need to buy another one.