I would say there is a reasonable dip in quality. It's lighter than my old Model M's and the plastic is not as nice, but all in all its still a very high quality keyboard compared against others today.

My biggest knock against it is that my keycaps are... strangely printed. The letters are not perfectly aligned with each other vertically, so that have kind of a jagged look. That could just be a problem with mine however, it's been a couple years since I bought it. Other than that however I love it.

I have two of them and while I like them, they are not the same build quality. In fact, there is a perceptible difference between an older and new one in terms of the weight including thickness of the plastic casing. Functionally however, I have had no problems and would definitely recommend.

No, it is no longer a combination self-defense weapon and keyboard. The buckling spring action itself is still decent but the build quality is much worse, and the melted plastic rivets that hold the membrane have a bad habit of breaking or flexing and rendering keys unusable over time. You can address the rivet issue by drilling with a pin vise and using screws but be prepared to spend a day doing it since there are something like 50-60 rivets.

There is someone that was doing a reproduction of the Model F (the earlier and more robust XT keyboard prior to the M) but they're quite a bit more pricey.

Here's a review: https://www.youtube.com/watch?v=-A-vRZth7SI . The Unicomps also feature in this overview of the Model Ms: https://www.youtube.com/watch?v=r5H58uudo1Y .