I have had first-hand experience transitioning my business into the MEAN stack. Here, I would like to share my 2 cents more from the business end. I am sure there are several technical folks out here with a lot of technical knowledge so I will take this approach from the tech + business perspective:
Node.JS is event driven – Event driven is great when you want to build an on-demand app like Uber, Postmates, OfferUp, Instagram. The inherent asynchronous characteristics of Node.JS is awesome to keep the server utilization to a minimum with the code being exercised when an event is triggered.
Micro-service design allows the developer to write small modular codes that do specific tasks only. It lets the code be truly object oriented and modular allowing for high usability. This micro-service design has to be used effectively because if the code that you are processing in your Async Task is too long, it can block the NodeJS thread and since Node.JS is single threaded your CPU is processing 1 task and delaying others. The latter is the only drawback of NodeJS, if you need a lot of data processed then you would rather use Python or maybe even PHP 7 for that matter. Node.JS is not the script to use for data heavy tasks.
The Java Script server is lean, fast and way more efficient than the Apache server in say PHP.
Node.JS has several NPM modules available in the Open Source community. Your developer just needs to be smart enough to google and choose the right modules. They can write code to stitch them together, therefore, accelerating your development quite a bit.
MongoDB is awesome and actually very easy for any developer to understand. The good part is that the write to MongoDB is really quick and does not block the server thread. MongoDB is evolving really quick with data aggregation, replica set, watcher, and timeout feature is very useful for mobile apps.
Angular 1.0 was good, Angular 2.0 was OK but Angular 4.0 is great. My website load time dropped from 6 seconds to 2 seconds by porting my website I deliver to Angular 4.0. Angular 4.0 has some great improvements over Angular 2.0. It is highly recommended porting your site to Angular 4.0 ASAP.
Angular 4.0 is facing some stiff competition from React.JS, but from a business perspective I prefer to keep in line with the MEAN and so we continue to use Angular 4.0 over React.JS.