I have some experience; I used mine at least five times last year. It's a duplicate of Rick White's system but it is not affixed to the bottom of the front crossbar, where it would compromise my tramp.

You need more leverage than the 90 degree extension, that's why Ricks' (and mine) uses swivel blocks off the corners of the front crossbar. The bar attaches to the bottom of the mast extension. See attachment