Those "big side pouches" aren't that big. Here's the vest with stuff in it for size reference:
The radio pouch isn't much bigger than a mag pouch, and located in a weird spot and those smaller pouches in front are probably too small to even fit one mag (and it would probably fall out easily if it did fit).
Drop pouches aren't that expensive, specially if you're buying repro. Save yourself the hassle. If you end up losing a mag you won't have saved anything in the end.