The most recent cheap used Express gun I bought (last week, $195 + tax, with a 20" RS ImpCyl barrel in place) had dimples. No big deal- I'm leaving them in place, since they don't bother me. That gun won't be wearing a magazine extension anyway. A shorter stock and a better recoil pad, yes- but no mag extension.
I've seen too many guns with bent or warped magazine tubes, erratic feeding due to parts of the dimples left in the tube, rough spots etc. from DIY attempts to remove dimples. Then there comes the hassle of making magazine caps and magazine springs stay in place without the mechanisms to keep them there. IMHO it just isn't worth the hassle- and yes, I have drilled out a couple of sets of dimples myself years ago. But I'm too old to have patience for the hassle these days, and I won't be doing it any more. For anyone else, of course, YMMV.
fwiw,
lpl