Knut's system using a cam cleat is interesting and I saw it before purchasing my Mast Climber. It doesn't allow for solo use though. I don't like going up solo, but I've done it a couple of times when I needed to get something done and couldn't get someone to spot me. I'd also watch the load rating on those cam cleats, a standard Harken 150 is only rated to 300lbs. The one in that photo looks like it might be a Ronstan, I can't tell if it is the medium size (275lb rating) or large (510lb).
I didn't make this system to climb solo, but in combination with other climbing equipment in can be done.
I'm not so concerned about the load on this cleat, it's only an aid to make climbing easier for the winch person (not a safety device).
I'm always using two halyards while climbing the mast.
I don't remember the make/model of the cleat, I reused some spare parts in my rigging bag and the plywood is also reused.