Has anyone used these lifters ?

Anti pump lifters are exactly what the name implies. They will not pump solid at high RPM and cause valve float like a standard hydraulic lifter. But to run them, you must run either zero valve lash, or even a little lash like .002"-.004" like a solid cam. And of course, there's usually a little noise involved. I've never liked them They are a kind of "bridge" if you will between hydraulic and solid lifters. I just make the jump to solid and be done with it.