I picked one of these up as well. I was originally looking at the Spiritus, but they don't seem to ever be in stock anywhere in multicam, or at least not all the pieces you need. It is a little obnoxious that you have to buy every part separately, but I get why, considering the adaptability.
What redirected me to the d3crm was:
1) the side mounted pistol mags. With Spiritus, if you opt for 2 pistol mags in your config, then you only get half an admin pouch. If you want a full pouch, you give up the mags. With the d3crm, you get both.
2) zipper pouch vs velcro. Velcro is loud. One of my intended uses is hunting, and I don't exactly want to be ripping open a whole front flap of velcro anytime I want to access the contents of the front pouch.
3) d3crm uses the kydex inserts to make reinserting mags easy. Admittedly, I didn't try the spiritus mag pouches, but it just seems like elastic will be less cooperative than a wide open pouch for quick reinsertion.
4) the d3crm is designed to work seamlessly with the haley flat pack hydration system/assault-ish pack. The spiritus might or might not fit it, but it wasn't designed to.
5) it was a little cheaper than the spiritus for the configuration I wanted.
That being said, I went with Spiritus' SACK because of the stretchy front pocket and non-full opening main zipper. It fits the d3crm perfectly.
I also picked up a little Maxpedition 3x5 velcro pouch as a pouch-within-a-SACK boo boo kit. It fits what I needed it to and sticks right into the SACK, leaving room for other stuff.