I still have a bunch of Tapco 20s, some of the first mags I bought, before I discovered Hungarian Tankers.
Always ran fine for me, great for running corrosive ammo. They all needed to be filed down to fit, wider than surplus mags.
But not so popular, and with PSA selling new Croat steel mags for $10 and cheap AC Unity mags around, $3.50 is probably about right.
Wasn’t that long ago you could buy new Tapcos for $6.