YES!! They would be FANTASTIC!! Here is why...
A very high end, high quality company, Creative Proucts aka C Products is soon to introduce a VERY nice SS Mini-14 mag. This WILL happen soon and will solve the mini-14 mag availability and quality issues.
It would count as 3 US parts.
It requires no modification to the weapon.
The mini-14 mags can be used with AR15 mag web gear and pouches and mag-puls (the original kind).
The adaptor can be made to function as a sort of mag funnel to help ease reloading.
In fact, the only thing that could possibly be better would be an AR