I own an MS-1-66, big set of wheel, big toe plate. It lifts 1200 lbs.
The big wheels work great on gravel and grass. The wheels also work well as a fulcrum to balance the load.
The big toe I have not seen a great use with as pins/vids and boilers* don't need it.
Yep, moved a 600lb boiler down the stairs last week with mine. Scary shit. But it does its job. Love it.
The only issue I have seen is that it would be nice if you could lock the wheels from moving when going up and down stairs. The issue is when you have tall items and are leaning way back to center the load or clear a bulkhead threshold, the freewheeling wheels can/will shoot forward if your lifting feet lose traction and you can end up pulling your shoulder out of socket trying to stop it from flying down the stairs. Talking from experience, one case of tendonitis and a cortisone shot later.
Escalera used to make a braking kit but I can not find it reference anymore. I am planning on drilling a hole through my wheels/frame to be able to insert locking pins.