My buddy uses them and loves them, they are fast and secure.
I'm using a different system, I've got 3 machines one behind the next on the trailer. I found the
Fastrap works better for me in this case. It takes about 20 seconds to tie or release each machine and I can just drive over the straps in the rear while loading/unloading the front machines. I found the best price at Sportsman's Guide.
The Prolockers would require that I remove the boot each and every time which would add up to lost time. For a single machine application I think they'd work just fine.