I am trying it out and keep getting stuff I'm not expecting. It is presumably the way I expect it to work is not the way it actually works, and I'm not sure I want to have two different realities to choose from depending on which app I am using.
As a trivial example, I type '12' in decimal mode and '=', click the HEX button. I expect to see 0x0C (or similar) but instead I see 0x12. My FX-991 in BASE-N mode acts in the following way: when entering the number in decimal mode, pressing HEX before hitting return will simply change the entry mode to hex (so 0x12). After hitting return, pressing HEX converts decimal to hex (so 0x0C).
OK, I want to convert 12 ft to something. So, back to decimal then select the conversion pane, select Length... Foot. The answer is "~39 ft + 4.440 944 882 in".
It's probably very cool if you operate it how it expects to be operated but, personally, if I'm not 100% sure it's showing what I think it should then I can't trust it.