For App Engine Google shifted functionality, increased prices and overcharged. They kill or effectively de-emphasize projects at will. This creates a risk of another parse migration. The open source parse is more reliable as you can switch vendors easily.
The content is deployed immediately through the Firebase CLI. Once it's uploaded, the content is served immediately. If you have made a mistake, you don't need to re-upload a new version, through the Admin dashboard you can easily rollback to a previous version.
In order to store sensitive data safely on Firebase, you first have to encrypt it. But by storing encrypted data on Firebase, you can't query that data easily unless you use something like IQrypt
Google acquired Firebase in Oct. 2014. This gives Firebase a degree of trustworthiness in their service and future support since they are backed by such a large company.
User registration with Kinvey is pretty good and usually works without any problems. It's also very easy to use, you simply pass the username, password, email, etc. to the required method and register a callback that returns whether the registration was a success or a failure.
Same thing is done for login and logout as well.
Setting up a backend for an app with Kinvey is very easy and takes minutes. All you have to do is sign up and through their graphical interface follow all the steps, which boils down to creating tables and identifying the type of data that is being stored.
Then you download the library, integrate it with your app and initialize the process with one single line.
Kuzzle has no hosted version. In order to use it, you have to install it to a remote machine. This can be cost-effective but it also adds overhead because you will have to take care of the hosting and backend infrastructure yourself.
Since Kinto is a self-hosted solution, it can be used to store sensitive data (emails, financial data etc...) safely, since only the developer has access to the backend.
Mozilla uses it in production to synchronize security settings for Firefox. This means that the product should have adequate support for an extended period of time due to Mozillas use of it.
In order to use kinto you have to download it and host it on your own server infrastructure. While it does help you avoid outsourcing your data to a third-party, it also adds the overhead of having to maintain a backend for your app.
For companies or large teams of developers, where there are multiple projects being worked on at once, you can choose permissions for any developer and decide who gains access to each app on the backend.
White label-able with the agency brand, multi-tenant allowing all apps to be managed through one view, but a filtered permission based view for each client.
Kumulos is lacking in the documentation department. A lot of things are explained in just a few sentences, with many things even being absent entirely.