You are correct, Velcro cummerbunds suck!
I have been running the FS cummerbund for 4 or 5 years now, it makes a massive improvement in the APC. The whole thing goes on and off with ease.
On a side note MRC/VS also make a PC adapter that allows you to ditch the cummerbund if you don't need side armor, which also greatly aids in cooling.
Or I have, in the last week, just started to run the MRC tactical back panel with a plate sleeve, I have only been able to train with it twice as of now, but this set up is showing great promise for a ultra light (drops 2 lbs over my APC/FS tubes set up) armor caring system, but you will need to run a chest rig that is compatible with the system. The shoulder straps on the tactical back panel are actually more comfortable than they look, the stiffness and with of the material is good and so dam thin! But again I have only about 8 hours using this system, and I have not yet used it with a ruck on, so only limited training with it. And again if you are required to wear side armor, this will not work for you.
Hoping to train with the simple set up again tomorrow. Have to be back in the APC over the weekend as the training environment is far more energetic and full armor is required on Friday-Sunday.
Overall, this scale-ability is what I really appreciate with the MRC APC as I can take it from a full PC with side/groin armor if we are breaching or strip it down to just minimal rolling gear with front and rear plates/backers if in the mountains for several hot days or if the environment does not require armor, ditch armor all together and still have the same chest rig.