I will third what Th3Pwnisher and punnyguy said about "feel".
I've done my RDL's a bit differently over my training career. I've done them with heavy weight before, as heavy as I could manage. That was before I understood the concept of assistance work.
Lately I have been using low-ish weight and really going for the hamstring stretch and then exploding up with a hip thrust. I really feel it in my hamstrings and glutes, unlike when I was grinding out heavy reps. I wasn't sure where I was feeling it then, I was just doing what I thought was an RDL with as much weight as I could manage.
My form may or may not be good. I've never sought an opinion on my RDLs, nor have I taken video of myself doing them. I can say, with absolute certainty, that the risk of injuring myself doing one with the weight I'm handling now is as close to zero as any lift I do.
RDL is a great assistance lift!