R8 Collets fit R8 Spindles - ER Collets fit R8 adapters CT BT NMTB HSK KM and a myriad of other Adapters, so a set of collets could cover a few machines in a shop, provided each had the corresponding adapters.
We pretty much use ER Collets exclusively because of the accuracy. These Collets collapse ER 16 range of compresion is 1mm for sizes larger that 1mm. I've found that the holders for ER collets are more compact that that of say TG collets.
"It's only funny until some one get's hurt, and then it's just hilarious!!" Mike Patton - Faith No More Ricochet