I actually like the S&B brass for it's snug primer pockets. I prime on a Ram Prime setup, not on the progressive press, so it's easier to feel the differences in primer pockets.
I load a lot of my ammunition on progressives, but I'm running already sized and primed brass through them, since I insist on cleaned primer pockets. I've had primers not seat completely due to debris buildup in the primer pockets in the past, and made the decision to never have that problem again.
As for loading MagTech and S&B brass, it's good brass. The MagTech is made in Brazil and the S&B is made in the Czech Republic, but they're both owned by the same parent company. Perhaps some reloading tools are more sensitive to differences between brass than others, but I don't have any problem loading any of them on my presses.
Hope this helps.
Fred