My friend Brian M. sent this picture to me. He and I always like higher capacity especially for USPSA and 3Gun. Around the same time as my Scorpion Evo3 +10 extension, Brian had the idea to make an extension for Colt/UZI SMG magazines. It is a +8rd extension making the Colt/UZI mag hold 40rds of 9mm. He drew this up and 3D printed it in his home. He successfully tested it fed all 40 rds.
9mm ARs are becoming increasingly popular. Sure you can get some that use Glock magazines but there are still a lot of guns out there using the Colt/UZI pattern magazines. I see these becoming very useful and not in just AR-9 but in 9mm Tavors or any other 9mm carbine that uses UZI mags.