I think that bitaxe will be less powerful than nano even in the best version of it, but I value others thinks when buy a product, who build it, how is build, etc, and just only for that I went for a bitaxe, all open source, open hardware (not all, but it's something).

Maybe if it's your first time, the old bitaxe could be a good option, battle tested, no new software, simple logic (one chip), use for a little, configure pools, check noise, check configurations, change voltage values (if you want), test... and then move into the next new thing.