I tried one of those Dieter single-point bungee slings, and I went to do a secondary transition and as I was moving, the rifle bounced around a lot and sprung up and cracked me in the mouth. I almost chipped some teeth. Needless to say, it went off the weapon right away after that.
Single-point slings are handy for shoulder transitions, but they're designed for use with subguns. They work decently with shorter SBRs (like a Mk18), but if you go to a longer rifle, they have a lot of failings.
If you fancy a single-point, look into Magpul's MS3 sling (out soon). It uses no bungee, so it won't flop around.