That connector is the Amp Enerflex. I have even seen it suggested that they could be used in stick built homes as a way to deal with the old 60c wire ceiling box problem. 334.21 is somewhat ambiguous on this.
http://www.ampnetconnect.com/product_cut_sheet.asp?grp_id=2307&path=0,2299,2307&pn=020816902
