I am a lefty with an Impact. I don't have any issues with the mag. It's out of the way and doesn't get my attention when shooting. I also keep the cocking handle OEM. I like it better on the right. I never have to take my left-hand off the grip/trigger. Speed shooting style. Also, I wouldn't want the mag on the left side.
I held off for years buying this gun because of being a lefty and thinking FX didn't care for us with a non-swappable handle, but for another $125 you can buy a left-hand cocking block. I still feel left out though with that (no pun), but didn't need it after all. The cocking is so easy is why. Almost zero cocking force.
I go back to my Marauder which has left-hand cocking and I don't like that now lol.