Just tossing in another opinion since the company has a free shipping deal this week.
I just replaced the d-pad myself. Gonna give a few tips first. The process was a bit more difficult than I expected. A credit card and folded post-it note worked well for removing the battery without damaging it in any way. I wasn't able to remove the power toggle in any comfortable manner and just sort of took the silver IO cover off from around it. Start on the side opposite, work your way around to the power switch itself to pull it out from under/around. Helps circumvent the entire issue with snapping the electrical part. I didn't actually disconnect the ribbon cable (couldn't find a comfortable, simple way to do this), and instead just gently lifted up the board until I could push out the original d-pad and push in the new one.
Basically, just be patient and fairly gentle with it. Make sure any force you use is well controlled.
As for my impressions, I'm feeling a bit mixed on it. I'm not too fond of the grip material - I'm sure it's because of the 3D printing process, but it feels a bit excessively rough to me. Each part of the pad feels a bit thinner than I expected as well, but that's not really a bad thing. The area where it let me down is with diagonals. They still
don't register as cleanly as I would like. It seems to be getting better with repeated use, but keep in mind that it's certainly not perfect yet. I'm wondering how much of this is more an issue with the membrane and less an issue with the d-pad.
Overall, it's an improvement over the original. Due to a lack of experience, I can't really give any input on whether or not it's better than using any other d-pad such as the original Game Boy's. Here's a photo of the end result.
If numerical ratings help anyone visualize, I would say that the original d-pad was probably a 5.5, this is more a 7. Both are functional and usable to be sure, but neither are especially excellent or perfectly responsive.
I might end up replacing the buttons just for aesthetic consistency. I don't really have any issues with mine though aside from the fact that they letter printing is slightly off center on some.
Edit: Later in the day, had more time to play with it. Some of my complaints are gradually resolving themselves - I think part of the issue was that I was still approaching the new d-pad like I did the old one. Want to reiterate that it's still not perfect, but I would give it more of a 7.5-8 now. It's an improvement and was worth dropping the cash on.