O2 measures well, it is simply an amp based on the objective performance, it has enough power to use for all thing, it has internal charger and it can be used as desktop amp but it can get boring real quick. Quickstep has small size format, very clear high and tight low, it is designed by Dr Meir who knows what he is making so you can be sure objectively it will perform well.
If I was to go back I would just get the quickstep with a good 15 volt PSU for home use and be willing to buy 9 volt battery from time to time when I need to use amp outside which I rarely do.
Yeah that's basically what I'm planning to do. But what exactly is a good 15 volt psu? Will the adapter that comes with the O2 for instance, work with the quickstep?