They appear to be pro-mag magazines, and are probably made for 12 .40 S&W rounds. You can get 17 9mm rounds into factory 12 round XD .40 mags. I used some like this for a while, and it worked well, but sometimes the 17th round sat too high in the mag.
They are probably 3rd party Beretta Mags modified to fit an XD. I have some that were sold by SA early on during the ban (mine are from Mec-Gar I think). They have a small caveat, you can not slam tha magazine into the gun, if you do you damage your ejector and extractor since the mag is too long. The mags must be put in slowly to avoid this. Now this guy may have fixed that with the extended but plate, but I am not sure.
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