There are no negatives to the on/off switch for me personally but I don't mind either method.I like the "on/off switch" on the Ampio. Looking forward to your impressions of the ES100. Are there any negatives to having a switch like that? It seems like it would be a faster/simpler method, and if there are no negatives, then I hope that @wslee considers replacing the on/off button (that has to be held down) with a switch in future models.
I had about 30-40 minutes with the ES100 last night, just used it straight out of the box and haven't even opened the app on my phone yet. I paired it with my Sony ZX300 and my early impressions are very positive. I actually don't mind the plastic materials although I don't know how it will hold up physically over time. In terms of sound it's easily as good as the Ampio if not better (haven't A/B them yet). By the way, I haven't tried the balanced output yet, just the 3.5 SE.