Any help identifying what this is? It fits perfectly in a Glock 19, but is TOTALLY un-marked. No numbers on the holes, but has 12, just like the G19 15-round magazine. No Glock name anywhere on the mag or floorplate. No caliber designation or marking anywhere. It does appear to have the pre-ban U-notch at the top, but does not appear to have the metal insert that my other Glock magazines have. Any info would be appreciated...including Fair market value...I paid $20 for it at a LGS and hope I didn't get smoked! Thanks in advance!