If anyone is concerned about not hitting the lower back when doing DL's from knee height and above, you should be. Might want to throw in a few sets of GM'ings or even SLDL's (off the floor) among the mix, at lease once a week. GM'ing are an exceptional exercise for improving the core (very over used word now in the strength training world..for good reason) lower back strength and has been known to improve anyone's squating abilities. Another reward from including them can be much improved hams. That also goes for the SLDL as well. Always train the abs just as hard (heavy) as the total back area. Very important for strength/muscle balance and also can guard against any potentional injury.
I agree with HedgeHog on all points except for the deep DL's. Though a supplemental exercise for PL'ers (and strongmen) who are well versed in the bio-mechanics and form of the lift, most BB'ers will not have a clue as to how to correctly preform this deeper version.. The DL it's self take a lot of time to just learn the basic's of the lift. Most BB'ers (and others) don't seem to want to bother with that, from what I've seen of them. Or else they will think their doing in right, which chances being, their not. This advance version, in my view, should only apply to experience lifter's or people who have a hand's on coach or trainer around to show the correct style of preformance.
Quite a few BB'er will complain about how they hurt their back from doing DL's. Or it's a dangerious exercise, the back get's too worn out too soon, back pain, etc. Fact being,in most cases, they just do not know how to preform this highly rewarding exercise ( not to cast any negative vib's on a few BB'ers I've seen workout, but some would have trouble chewing gum and walking at the same time). There starts the potentional for injury. Of course their are some trainee's who have defective muscle/spine problem to begin with and can be bette off avoiding the DL all together. The DL is not meant for everyone. Good Luck.
Glad to learn that those rubber bumper plates are used world wide. They can also boost the confidence because it looks like your lifting railroad wheels. Also great for doing Hooper Dl's and the like. Good Luck.