I have an SQ-A that I've been using for almost a year now, and I really like this camera. For the first 6 months or so I was fighting light leaks in the backs. 5 backs came with it, and I discovered that all but one were cracked where they face against the camera body. This piece of the back is plastic, and secured to the back by screws, with one screw above and below the dark slide slot. The backs like to crack at those screws. I think this was caused by forcing the dark slide in at an angle, or with the back removed, as there is a detent that must be pushed in to insert the dark slide with the back off the camera body. The guy that had this system before me was definitely hard on it. He could probably tear up a bowling ball, if you know what I mean. The 5th back in this batch of backs needed new seals and should now be as good as new, although it's a bit ugly.
In my opinion, the backs are the most likely to cause headaches, but once you get some that work, they work well and it's a good system.
I have the speed grip and WLF, plus a dead AE Prism.
Dave