I've only ever had the D rings and in answer to Biggles' query, I
do clip the end onto itself.
In regard to the quick release buckles I think some (or all) of the BMW helmets come standard with them.
The quick release buckle
attachment was doing the rounds of some of the NSW Ulysses branches about 6 years ago, then they seemed to go quiet as there was some conjecture about whether they'd do the job. I hope they have and
are legal, as those D rings can be a real pain at times, especially in winter when the old fingers get a bit stiffer with the cold.
If you search eBay, you come up with many variations, so it's just a matter of trying to work out which will suit you.
The text below tells us about quick release buckles attached to
new helmets but I havent seen where it's ok to use the quick release attachment on an existing helmet
http://www.rta.nsw.gov.au/roadsafety/motorcyclesafety/motorcyclehelmets.html