Wayne,
not worth their salt! We`ve tried them all & some work well but they`re all 2 inefficient.
We had a customer up the Dandenongs who insisted we mulched all the prunings on a large pittosporum hedge.
We did, by the time we had finished (using a large industrial mulcher,not a chipper) including the hire cost, he could have bought high quality composted mulch & been miles ahead financially.
If its only small stuff , stick with running the mower over it.
We dispose all of our green waste at Envromix Keysborough
Cheers Dean.