Despite having it a few days, I haven't used mine in vengence (just been to busy during the day and evenings). However over all it is a really nice piece of kit. Personally I would have been happier if they removed the extra keys from the right (or positioned them elsewhere), and made the keyboard bigger/more central. In terms of typing I am basically finding there is a learning curve for me, I am used to using certain thumbs/fingers on certain keys, but because the keyboard on this is to one side, it actually makes sense to use different thumbs/fingers. I have started making an active effort to do this (in particular using a sensible shift button) and immediately it is feeling way better. My gut feeling is with a bit of use, the keyboard will generally be fine, and you'll end up not thinking about it too much. This doesn't mean the Pyra keyboard won't be "better", it just means I feel that with time the keyboard won't be a stick point with the GPD-WIN.
There is something quite surreal about having a Windows machine in this form factor, I run Steam in big picture mode and have access to loads of games, many of them run directly on the hardware, and so far my use case has been in the office, or at home, in both cases there are desktop machines with Steam games on, so I can stream them onto the GPD-WIN and play the latest/greatest on the small form factor. Can alt-tab out, adjust volume, browse pages, well I can just do anything really, no waiting for people to make specific ports, can use Skype or any other program I want, so yes, it is a nice feeling. The mono sound is honestly a bit weird, I mean it is fine, I understand why it is done like it, but it stood out ot me right away. Of course headphones work as expected.
I somehow feel basic Windows stuff can feel a bit slow, i.e. Steam takes quite a while to load up, some webpages seem to struggle a bit, obviously I didn't expect it to be 12 core X 4GHz performance, but I did expect perhaps a little better on that side (although maybe a few tweaks will help).
Soon after getting the device, I allowed it to do a Windows update, left it over night, came in and it was stuck on some percentage (34% maybe?), from doing a Google search, at this point the device should have rebooted, not sure what happened, anyway, cycled the power, the updated continued and finished and all was well.
I think the build quality is very good, anyone who doesn't own one who is commented I would question, I say this not in a mean way, but in terms of I feel the device is a lot more impressive in real life than a photo. It is comfortable in my hands and games play nicely on it. The DPAD certainly doesn't feel amazing, sort of slidey/spongey, but that said, I was doing a lot of gestures (for fighting games, RIGHT, LEFT, BUTTON, etc.) and it always did what I expected. The triggers feel a bit cheap to me, like quite light/clicky (hard to explain), but have always performed as required.
So bottom line, Q/A:
Was it worth it? For me, 100% yes, for what I paid, I am very happy with it as a little toy.
Will it replace my Pandora? Honestly, the answer is probably yes, I love my Pandora, it is in mint condition and has been looked after incredibly well, however it is a bit long in the tooth now!
Has buying the GPD-WIN made an impact on whether I will buy a Pyra or not? Possibly? I was on the fence before (wasn't sure I could justify the money given how much I anticipated using it), in some respects the GPD-WIN means I don't need a Pyra, but in other respects having one cool little handheld has made me want to get another cool little handheld.
Does the GPD-WIN have decent performance? Well yes and no, it plays a lot of games, but a large number of games it 'plays' really aren't at a frame rate I'd be happy playing at. So I think you need to be a little careful about expectations about what you can play on the device if you like decent frame rates (I appreciate some people are happy with variable 15-30 FPS, but that isn't really me on the whole).
Is the GPD-WIN better or wose than the Pyra? Ha ha ha, of course I can't answer this! If you are on the fence just go and buy both, sure it means paying more money, but just forget about that, beg, borrow, steal, get both devices, enjoy them, live happy, die poor!