In reply to A Longleat Boulderer:
In their defence they sent me a replacement plastic clamp bit foc for my split one.
I've found it's fine as long as you a) use the big fat sections first and b) don't extend them all the way if you don't have to. Keep a few inches of each back for stability and it doesn't stress the plastic anywhere near as much.
However not long after I replaced the broken bit someone at the crag borrowed it, and, predictably extended only the smallest, weakest, section and split the clamp 🙄