Tbf I've worked on loads of firms who use readylok arms if their using van thiel extendable transoms ( I say van thiel as he was the creator of extendable transoms) but yeah lots of firms think they should be used together, and as for the 3 board extended transoms can't happen because of the extended bit won't bear the loads properly even with 2 inside boards,so I was told by a boss whose also a designer and was one of the first in the UK to use van thiel, even Mr van thiel himself payed for my boss and supervisor to fly over to Holland and meet him and then was taken around a few van thiel sites as he's actually a working company over there, to see how his system works etc,and the only size tube van thiel uses with his tubelok are 13ft,8ft and 5ft and of course his extendable transoms no other size tube he says we don't do that spaghetti scaffolding with all different size tube,you can accomplish it with 13s,8s 5s because as you know you ain't got to stagger joints with his tubelok,anyways my boss asked about smaller extended transoms and his reply was about the weight, on the end of the smaller extended transom