The 38mm or inch and a half is offcuts from overhead gantry decking, comercial use stuff. I've got some and it's, well it's ok, the grip is never great and it creaks if you use it as a bridge, better to use 2 thicknesses.
To be fair I don't think the 2 inch stuff is any better fro grip, some is wirse as it's not gritted.
At the end of the day I don't think someone went out and invented the stuff for us to use, I think they tried to find a market for all their offcuts.