I haven't noticed any problems with multiple simultaneous button presses on the XD, whether in Retroarch or other emulators.
Having said that, I've owned two XDs now and neither of them had very satisfying dpads or buttons. They always felt mushy and unsatisfying. They aren't absolutely terrible, they aren't unusable, but they're not great when compared to either a 3DS or a PS Vita. Although plugging a wired gamepad or arcade stick into the micro-USB slot is an option.
I have had a screen failure in one of my XDs effectively killing it, and although I haven't encountered it, they do also have a reputation for critical battery issues while charging. If my current XD dies on me, I won't be replacing it.
And while the GPD Win looked interesting, the accumulation of issues I've encountered makes me really hesitant to spend $400 on a GPD device. Maybe those are more reliable, I haven't looked into the GPD Win's reputation at great length.