Last summer I had the chance to do some departure failures and low approach engine failures. Let me just say that they happen very quickly in a Robbie!
The approach failures were basically as has been described above--you just need to take them as you'd be doing them had the failure occured higher up. You'll probably be going much slower than in a regular auto (say, at <100 ft) but that just translates into waiting 'til you're a bit lower to flair.
However, on the departure failures, things happened VERY fast! Even when we counted down I'd be dropping the collective (fast!) as we started rolling off the throttle, and we still often got a low-RPM horn. Suffice it to say that you _don't_ have the 'leisurely' 1-2 seconds you do during cruise
I'd recommend that you try it sometime so you realize the urgency during high power maneuvers, but be ready. Could you fly someplace else (another field) to do it, or is there a restriction against doing this in the heli you fly?
As to the altitude at which an EOL is not possible, I'd imagine you can do takeoffs and approaches that will always allow you to make it to the ground safely in an engine-out condition. I wouldn't suggest hovering over your house at 50 ft tho!