The Tapco mags can only be inserted with the bolt open. So if you remove a mag and then close the bolt, you'll have to hold the bolt back while you insert the mag to get it in. It's not a big deal. Just leave the bolt open - it locks open on an empty mag anyway.
I'm not saying the SKS is anything more than it is, but like I said, my experience with the Tapco 20 rounders in my Norinco has been excellent.
That said, I recently decided to take the Norinco back to its original form. I bought the little beast probably 5 months ago with the stock in horrible shape, so I immediately ordered a Tapco T6. Had a lot of fun with that stock. Then I decided I might try taking the SKS out deer hunting - so I bought an ATI Monte Carlo, got a scope mount to go on the side rail that my Norinco already had, and mounted a Weaver K4 to it. Before I even took it out, I decided it was time to go back to basics - had a little fun refinishing the original junky stock - took a lighter to it and made some stripes. I've got a couple of replacement stocks on the way. But you know, I never even shot the SKS in its original form, so I'm going to give it a shot.
The moral of my story? There really is none. If you want to try a Tapco mag, they're fairly cheap - if it works, cool - if it doesn't, buy a bunch of stripper clips for the SKS and invest in an AK for detachable mags. I'm about to build a Romanian AK and waiting for my local store to get a Saiga for me.