9 Sp rear mech on a 10 sp cassette

Has anyone tried running a 9 Sp rear mech on a 10 sp cassette with a 34 T sprocket? Iv read other bits n pieces on it but was wondering if anyone here has actually tried it?
I often wondered how a guy, who so obviously looks after his bike, could end up ****ing it into a hedge because the gears were slipping and have the drive train explode at the start of the Nationals ....... I think I'm beginning to understand ........ leave it the **** alone Oscar!!!
As long as your shifter matches your cassette you'll be fine..

The shifter controls the amount of cable pull... the derailler just does what its told to do by the shifter..
Just to correct myself there.. it won't work with a Shimano 10 speed shifter / 9sp shimano derailler.. no surprise there really.. Shimano muck doing what it does best... being difficult and finnicky...

But... it will work with a Sram 10 speed shifter / 9sp derailler.. both have to be Sram of course..

Good old Sram... You just can't fault it..!