I do these. I just call them RDL's.
Keep your knees a tiny bit bent. Keep the bar as close to your legs as possible. It's pretty hard to round your back, which is what most people do with Stiff Legged Deadlifts
. You can still pull a back muscle, but that's different.
It's really for hams, but it of course uses your back. I never had hams before I added these.
Just stick at a weight for a while, till you can do some higher reps. Then bump it up. I start at my 3 rep weight and keep going till I hit 8. (Well, normally I'm that patient). Try 6-10 if you just added them, and then ease lower, or go right to 3.