I could never find the 209-4s so I never tried them. I went the ACP route instead, and have no regrets. Blowback in my Omega was reduced to near zero, priming/depriming was a little easier, and accuracy seemed to improve a bit. Sure you have about $70 in upfront costs for the plug and brass, and you need a priming tool. But the primers are cheaper if you shoot a lot also.