I use these Xamarin products and are immensely helpful in helping C# developers write native apps in much less time than learning Objective-C etc. Keep in mind however that only some of your .NET experience is transferrable. For the most part you will still need to learn about how the operating systems and UIs work.
For anyone who writes code for a living these commercial products are worth their costs and support is excellent.
Oops, i did not know that, it is the iPhone hype that caught me then. Somehow I am not a big fan of Apple products. I have used those, but do not find the flexibility that Microsoft products have. No idea about the other products that you listed.
The fact is Moon is look beautiful from far. but when we go in, moon does not look pretty(I went there in dream). we have option to work with microsoft that is why they look crappy sometimes because of depth of knowledge about microsoft.