I will say the one thing I like about that gun is the locking coupler. I bought one and put it on my "Leak-O-Matic", and it delivers grease without half of it squirting out the side of the Zirk fitting. It's nice to be able to clamp it on while you're laying underneath the vehicle, and pump away.
But I can't vouch for the gun itself. Taking a chance by paying over a C note for a hand pump grease gun, that supposedly won't leak is a bit of an expensive gamble. And for that price it should have machined threads on the end cap..... Not rolled.