I couldn't decide between the TT350o and TT685o for my E-M10 so I bought both. I kept both. If I had to choose just one, I would choose the TT350. On the camera I only use the TT350. The TT685 is 1 stop brighter and much bigger/heavier (too much for in-camera use, IMO). The TT350o is powerful enough for indoor use 95% of the time (and if that wasn't enough, I'd rather bump the ISO by 1 than lug around a 685). I only use the TT685 outside of a TT350 controlled camera when the scene could benefit from multiple lights. Both flashes work very well together.
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