I JUST bought one for my Kel-Tek P-11 this past weekend. I haven't used it yet (live fire) but have a few observations: It is a little longer than the factory magazine bu about 1/8". The plastic on the end-plate isn't the only reason, the metal portion is simply longer. And, getting the 1st round in it requires a little finesse. Other than that, it seems to solidly latch in place and feeds (manually) fine. I will post how it works the next time I make it to the range (given the weather, it WON'T be soon).
I paid $22.00 + tax for it.