I'm using 10/20 straight stainless C-Products mags. They were WAY too short to grasp easily prior to my Dremeling down the dust skirts to get drop-free. You'll have to add Tactipul or Magpul Ranger plates
Curved or straight the 20 round mags work fine on the FS2000. It is recommended you have either a Tactipul, Magpul, Magpul Ranger plate, or something to help you pull out the mag (unless you remove or cut the mag's dust skirts for a drop-free. They are just barely long enough to offer about a half-inch of gripping surface. It's simply not efficient enough for fast mag changes.
I'm going for the D&H and C Product Aluminum magazines with Black Teflon coating. I'm also adding the MPRanger Magpuls on all of them. Its must have!