In my experience with the device, all of the major issues that I ever came across have been addressed. If anything, I experienced something where the device wouldn't come out of standby mode, but it's honestly so rare (I haven't had it happen in a very long time, now -- I think a few months ago was the last time) that I have completely forgotten about it until just now. It's easily resolved by flipping the switch on the back of the unit off/on again, though, so it's more of an annoyance than anything. With no definite steps to reproduce outside of it happens after being in standby mode for X amount of time (X = an unknown amount of time), Topping hasn't addressed that yet, and I seem to be the only one who has reported this, so it probably isn't universal.
I also haven't done a lot of messing around to see if there's anything of note with v2.14, so there might be an issue or two there that I haven't encountered simply because I haven't used/tested whatever setting may be causing a problem.
There's always going to be an issue (that's just the way things are), but I would argue that the device has been pretty stable for me since the last FW update. Others may disagree, though.
The only other thing to mention is if the friend plans to use this device on a Mac or Linux (though Linux users have plenty of access to things that will negate this issue), there is a data streaming pop caused by the XMOS USB chip waking up/going to sleep, but that is not something that is specific to this device (or Topping for that matter). It's a non-issue on Windows because the driver allows you to set the data streaming to be always on (which I believe it's set to that by default, now). It's a non-issue if the the TOSLINK, digital coax or Bluetooth inputs if the device is used as a preamp in a HT or small stereo system. This is only if you use the USB input on the device with MacOS, and largely only noticeable if it's used in a nearfield context (and even then, it's very subtle).
The workaround on MacOS is to either use a USB DDC in between the Mac and the DX5 II (I have used a Topping D10s, but a SMSL PO100 or PO100 Pro works) or run an app called Keep Mac Audio Alive (you can search the review thread for that) running in the background -- the app is very resource-light, so it's not going to bog anything down. The caveat with using the app is you have to remember to manually put the Mac to sleep otherwise the DX5 II won't go into standby mode since it is being fed a constant stream of data. This is not a concern if a USB DDC is used.
That's really about it, though.