Thanks Paul for this very interesting discussion, for people like me who are breastfeed(my traducer's word…) with the W technology of pull systems on the lathe more than any other technology, your comments about the ER system is very interesting.
Personally I'm using the ER chucks only on non rotating machines like the grinding use, and your comments open some ways when we have problems with the length for example, ER system is really shorter than pulled chucks.