I got three of the Tapco mags today. Like the steel duckbills, the Tapcos cannot be inserted or removed with the bolt forward, so far as I can tell. To insert one, you must pull the bolt back and then push up the bolt hold open piece with your finger through the mag well. My steel mags lock the bolt back after the final round has been fired, so that the empty mag can be removed. There are a number of differences in specs between the steel and plastic mags so one can hope that the new mags are an improvement. I will test them at the range very soon. I have never been able to get the steel duckbull mags to function with 100% reliability but I still prefer using them to attempting to reload witrh stripper clips.
Drakejake
Postscript: Granted that Tapco is close by in Georgia (I am in Nashville), they are fast shippers. I ordered Thursday, order was shipped Friday, and arrived today (Saturday) before 10:00 AM via FedEx. If they had used UPS, I would not have gotten the package until Monday.