a failing knock sensor will retard the timing and hesitate, bad gas mileage, etc. whether yours is failing or not we can't say, you didn't even mention if the check engine light is on and if the knock sensor code was recorded. if it is, then it should help. if not then you likely need NGK spark plug and OEM or at least high quality spark plugs wires, and maybe spark plug gaskets if they're leaking (plugs will have oil on them).
i've used a ton of ebay sensors, thing is they are so easy to replace (one bolt) and so cheap who cares if you had to replace it one more time...though i've never seen that happen. if you're worried, keep the old one in the spare wheel well. with a DOHC EJ25 that knock sensor is way down the list of probable issues you'll have in the future.