"Even so. A so-so magazine is fine for the range, I would think."
Of all of the 3Ks I've ever tried, they have all been incredibly poor. From standard caps to 30 rounders. (This is before the hi-cap ban so they were going for even cheaper than now if you can believe it.)
Making a mag that meets all of the critical dimensions is actually pretty easy. What's inbetween the dimensions and what the mag is actually made of is the problem. The 3Ks I had bought were usually softer in steel and some times thinner in gage, followers that allow nose diving, internal tube dimensions smaller than spec due to weld lines and slight bowing inwards of the back. A combination of the problems tended to hang up the rounds somewhere in the middle of the mag as the rounds nose dived somehow. Had one 30 round 3K that wouldn't drop from my BHP. Had to realy yank on it to get it out. Thankfully, the sheet steel was much softer than the mag chatch.
The problems were so great that it was a waste of range time and, if you're paying by the hour, money. There is a reason 3Ks and USA mags are so cheap. They usually offer a lifetime gaurantee too. But if you consider the postage and hassle to send their low cost mags back just to get new low grade mags in return, why bother? (And I think that is what they think the buyers will do.)
Some people, myself even, do, however, like to try things out for themselves just to see if all that is said is true. My suggestion is, you you do decide to get 3K mags, get only one first and wring it out before ordering more.