What are some drawbacks to using CrossRider as platform for developing extensions for multiple browsers?

As of 26th of September 2016 Crossrider is no longer providing its extension development platform as per this email sent to its users:

Dear Partners,

All good things must come to an end eventually and, regretfully, so does the Crossrider Extensions Development Platform.

After several years of collaborating with you, we have decided to terminate the service.

Please be advised that termination of the service is effective immediately upon publication or otherwise receipt of this notice.

For your ease, Crossrider Extensions Development Platform will remain available for another 30 days from 27.09.2016 for you to download your project code / source code / extensions, following which your data will be lost.

See below an instruction note on how to download the project code from our server for your easy reference; but kindly note that Crossrider is not able to provide further assistance.

We would like to thank you for all your support and trust throughout the years and hope we can have the opportunity to collaborate again in the future.

Best,

Crossrider Team

So I'd consider that a pretty big limitation.