Not long after the GRIII launched, I went to a Ricoh photowalk organised with a UK retailer, which started with the usual talk at such events and felt the III’s IBIS was useful in having the camera - certainly, it was a feature that was a must-have, or a near one, for quite of the few attendees, who I spoke to.
I’ve been to quite a few of these type of events and this one was similar to another one (Panasonic) in terms of people attending and how wonderfully diverse the crowd was, in terms of experience, knowledge and kit. Virtually all (including myself) hadn’t used Ricoh kit and the event was definitely a good marketing tool (plus a 10% off camera orders within 7 days). Not sure how many sales were converted from it, but my gut feeling was a decent proportion of people attending, based on talking to others and store staff. We were able to use both the GRII and GRIII on the photowalk - interest was really on the latter.
re: start-up time - I think it is PD good. On the walk, I did a couple of experiments where I had the camera off and by my side, then raising it as it was switched on, to see if I could make a shot that I wanted (e.g. as a couple of people were entering in front of me as they entered an arch) - and was able to make those shots; had the startup be a second or half, would have missed them. A slightly slower startup isn’t a dealbreaker for me, as in real-world usage, I’m not going to be switching on and off the camera that way - but sometimes, particularly, with friends and family, faster start-up to capture will let me capture the moment.
Re: converter lens - personally, I like when there are these sort of options available, but not sure if it’s something I would really get much usage out of. That said, when I had a quick go with the GW3, was rather impressed - and it’s good to hear positive things about it from someone who has one.