Just to set some expectations, this is a product in preview mode. Not everything is there that you would expect to be. For example, you can currently only tie the build process into GitHub for source control. If you want a full and complex build process that you need to modify, an app distribution method where you can attach release notes or something beyond the basics, it currently won't do enough for you. But what it does do is easy to work with, very intuitive and I have really not encountered any major problems other than trying to tie it to my enterprise MSDN account for table and identity services.
This appears to be a product that was started before Microsoft purchased Xamarin as the items they implemented first are what was important to Xamarin and not Microsoft as a whole. For example, while there are plans to tie into VSTS for source control, that has not been done yet. While there are plans to implement UWP apps, they are not in there yet either. Microsoft may have Cordova tools in Visual Studio (TACO), but compiling for Cordova is no where to be seen in VSMC. These things will likely all come in time but wasn't the focus of the initial pass.
The general features of VSMC can been summarized as follows:
Build Services - For iOS and Android. Soon to feature UWP.
Cloud Test platform - 1000s of devices in the cloud that can run your Calabash, Appium or Xamairn.UITests. Currently just runs tests from the command line.
App Distribution - Manage different versions of your app and allow testing groups to download and use your app. HockeyApp lite.
Table Services - A light weight front end to Azure tables storage.
Identity Services - A light weight front end to Azure identity services.
Crash Reporting - Track when your apps crash, seems to work for iOS, Android and UWP.
Analytics - Write custom events about how users interact with your app, also seems to work for iOS, Android and UWP.
In some ways I question the usefulness of the table services and identity services that front end Azure in anything other than very simple apps. There is not a lot of control over what is happening under the covers. I'd probably go directly to Azure's Mobile Apps for anything of consequence. However, if you want to stand up a quick app any your needs are really basic, the table and identity services may work for you.
I think it is fair to say the same about many of the things that are currently in VSMC. The most basic functionality is there but there just isn't much else. Some of this is likely to be an artifact of the fact that the product is in preview but also I think to some extent it is by design. For basic apps and people just getting into mobile and really don't have the capability to set up CI/CD build servers, HockeyApp, set up Azure, etc it's a nice place to get started.
A nice bonus feature for those without Macs and are doing something like a Xamarin Forms app, it can build the iOS version of app for you. The only other thing you will need is an Apple developer account for the certificate and provisioning profile and you can then use VSMC to build and deploy the app so you can install and try it on your iPhone/iPad.I've hear rumors that HockeyApp and Xamarin Test cloud will at some point be rolled into VSMC. It will need a lot of work and features for that to happen. I've also heard from the team that individual pieces of of VSMC may be able to be purchased independently. That would be good if you don't need the build services or cloud app testing but really want the crash reporting and analytics pieces.
Overall the product looks promising. If I were to position it I would say it is currently intended for indie developers and small start up companies without a lot of mobile infrastructure expertise. Complex features and ability to do customization isn't there yet but given this will be under the Azure umbrella those capabilities may come with time. I don't know the pricing yet but overall this is a product to watch.