I also have the deployment bag, but forgot to take pics. The inside of all sections are lined with soft velcro and it does come with the one fat movable velcro strap. In the pic on SIG's website you can barely see the strap behind the back sight. You can re-postion that strap to any position and it is all you need to secure the MPX.
Currently I have the SB Tactical brace installed on mine which is very similar to the Stock that SIG shows in their pic, and I have the Romeo 3 installed and it all barely fits in the bag. Before when I had the foldable SIG Brace installed, I could fit the MPX, Romeo 3 and a loaded / installed 30 rd. mag, but can't get the mag to fit with the SB Tactical brace. The three mag holder shown in SIG's pic is sold separately, but I think they quit selling it. Try to find one, it is velcro'ed and works great. I carry three loaded mags all the time with mine. This video below is what convinced me to buy one. It's done by Osage County Guns. I actually purchased my MPX pistol from them through Gun Broker, because they participate in the SIG Military / LEO discount program.
Hope this helps some.
The bag you want is the second one he demos.
