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As this technology's been used behind the scenes by Google for over 10 years, their native libraries can be considered highly robust.
Pro Third party support for multiple programming languages
Supports multiple programming languages via third party solutions.
The protocol includes versioning, allowing clients on older versions of code to continue to communicate with an upgraded server (i.e. clients and servers don't need to be upgraded in unison).
Pro Not widely adopted
If you hope to present your services to other companies this may be a drawback. REST (and "pseudo-rest" variants) has become the de-facto choice, with SOAP a close second. This means anyone connecting to your services would need to familiarise themselves with a new method of communication, and that they are less likely to have an existing toolset for such integrations built into their systems.
Pro Composite type extensions
A range of addresses can be declared as available without further definition. This allows third parties to use these spare fields for their custom requirements.
Pro No parsing overhead
Unlike JSON and XML, because data is exchanged in binary, there is little to no parsing overhead, resulting in significant performance gains.
Pro Open source
It's free, open source and licensed under BSD-3