Planning on knocking up a rollcage out of 50mm CDS

..... I've got one of these already knocking about vvvvvv
I've not tried it out yet as I haven't got the CDS, I'm slightly worried that the tube bender might just kink the tube
Anyone used a one of those to rustle up a cage or have you all used the mandrel benders (which I really cant afford

)
any info will be brilliant