I've never heard of Prolong. I'm sure it will help with corrosion resistance, as it is probably mostly oil. If you're thinking the claimed microscopic film will remain on the blade longer than a regular oil film, I am skeptical. There is no reservoir of chemical (as an engine's sump) to replenish the coating after it gets abraded by cutting and working the lock. Plus, who really knows what those snake oil products actually do. Lucas oil treatment and Restore claim to do similar things in an engine, but there's almost no independent testing to verify claims.
It wouldn't hurt to try, but make sure you don't use that knife for food prep. Who knows what kinds of chemicals or heavy metals are in that stuff. I've thought about using some Boeshield T9, which is a spray-on corrosion inhibitor used in the aircraft industry (and adopted by hobbyists for protecting machined cast iron surfaces), but I don't want to forget I applied the coating and then use that knife for food.
And if that Prolong stuff smells like most engine oil treatments, well that would be a big downside.