I am maintaining a comparison table at OXI One versus Hapax - Google Dokument feedback welcomed (please comment in the doc).
Manuel from Oxi Instruments gave it a once-over a few days ago so it should be accurate for the Oxi One; the Hapax side is stuff I gleaned from the manual.
Full disclosure: I currently own an Oxi but am not trying to take sides. I think its amazing but do find it a bit menu divey and am definitely tempted by the Hapax which seems easier to grok. They are both very capable. I wish the Hapax was also battery-powered and had the BLE; that makes the Oxi pretty killer with an iPad.