Shaver HD-10

I want reviews on the Shaver HD-10. There's a guy that has them at a steal of a price, just a few hundred dollars more than used ones. I want to outfit it on my CaseIH Farmall 65A since its very fuel efficient and the largest open station I have. It says the pounder needs 12 gpm, but my tractor has 10.4 gpm pump flow and 18.7 gpm total flow. It's an open center fixed displacement gear pump.

All I can figure out is it just takes longer for the ram to raise. The rest is gravity right? Never have owned a hydraulic post driver and can't figure out why the HD-8 only requires 3-4 gpm.

Shaver HD-10