To my knowledge, miss-fires have never been the issue with the 209 priming system. Fliers have been. The standard 209 primer is relatively hot and the theory is that the force of the primer lifts the sabot and bullet off of the powder before ignition. This creates a space between bullet and powder which causes erratic accuracy(i.e. fliers).
I've used the system (both .22hornet case and 25acp case)for maybe 8 years now with good success. The handling is an advantage(especially for fumble fingers like mine), I get zero blowback(fowling) in my action, and accuracy is outstanding. Granted my Encore shot very good before, but I did get the occasional flyer. GOOD SHOOTIN', Walt