Okay, I've been using my 664 for a couple years now. Now I just bought the 688 (3 weeks ago) 'cause i wanted the mix assist. The 1st most annoying thing is that it draws a lot more power than the 664. At least 50% more in my estimation. Also the battery meter is not as nice. instead of a bar that keeps getting smaller, you just have GREEN, YELLOW, then RED... And then it dies real quick. There are no voltage threshold adjustments - only battery type choices. I've lost battery twice durring shooting. Wish I wouldn't have got this thing - no big improvement over the 664... Also it won't interface with CL-9, or CL-WiFi, so I guess I'll have to keep my 788 for cart work.