Nice vid. I am looking at the MS3/ASAP combo as well. I am a left handed shooter too.
I’m a lefty, I use the urban ert 2/1 slings.
I’ve tried 2-point, 3-point and Single Point…What has been the most practical and comfortable is a single point with my Stark Grip…makes transitions :dance3: as a lefty…its perfect for me…if I was righty…i’d probably have a 2-point
I too am cross dominant, lefty on the carbine, righty on the pistol. Have used a Blue Force Gear Padded VCAS sling on both of my carbines for the last couple of years. Like Iraq Ninja mentioned, they are “robust” for what they do. Never had a problem with the slings interfering with the ejected casings.
Living in the “rain belt” of the Pacific Northwest, I just had to experiment with soaked slings. Ran one sling dry and the other soaking wet. The wet VCAS ran even smoother while I ran the acetal slider back and forth while doing transitions from strong side to weak side. The slider “squeegeed” the water out of the material and everything ran just fine.
Sometimes you just have to take the advice of our more experienced members and run with it. If it works out, great, you can howl at the moon. If it doesn’t,… “Hey Hon, how much we have in our checking account?!!” 
Being a true left handed shooter (pistol and rifle) I have tried all the the all above and the best solution for me is a Vickers sling. The worst setup was an HK factory sling on a HK94/93. That damn sling never worked for me the way it did for my right handed friends.
The Vickers sling works fantastic and alows me to transition to my right side quickly and efficiently. It also allows me to switch to my pistol and does not get in the way.
I does everything I need it to do and is inexpensive and KISS. YMMV.
Savvy sniper has one for a lefty. I ordered one and like it. Top notch customer service too. The missed my e-mail and hooked me up once it was noticed. Went over the top with the apology.