We shared our design with Miguel for feedback ahead of the release. He gave us a boatload of very high quality and informed feedback. Thanks! We haven't been able to act on most of it yet, since it relates more to what to do next than what we released just now.
We're hoping to see this NuGet package supported on top of Mono, too. As we've done previously, we'll share our tests with Xamarin to ensure consistent behavior between implementations.
Mono.SIMD has a few extra features that are missing from the current design, but they are not that important.
Microsoft has found a pleasant and easier to use API than we did. We have shared our feedback with them, and hopefully it will keep improving.