There is a very informative post about the asset from when it was released outlining all of its features on the Unity Forums, however for the most up to date information on new additions to the engine, it is best to check the Unity Asset Store page.
There are a number of different ways you can recieve support, but the easiest and recommended way is to join the discord server.
When the asset first came out it only cost $25 USD, but the price has risen gradually over the years with the addition of many new features and improvements. Furthermore, many users can attest to the hundreds of hours in developing time that this asset has saved them, allowing them to focus more time and energy into other core game mechanics.
The asset was released on the Unity Asset Store on May 22nd of 2018.
The short answer is no, the asset does not support infinite terrain, nor will this asset ever support infinite terrain. This asset has been optimized around having a fixed world size, increasing the speed of the engine beyond what would ever be possible with an infinite terrain engine. For this reason and the sheer amount of work that an infinite terrain engine would require (it would mean completely revamping the core mechanics of the engine), infinite terrain will not be added to Terrain Engine 2D. However will I ever release an infinite terrain engine as another asset on the Unity Asset store? Only time will tell.
All block data is stored in memory for efficiency, there is no dynamic reading from file. This means the max size of any world is just over 2 billion blocks, however the actual amount of blocks your system can handle will depend on your ram and processing power. It is also worth noting that the more features of the asset you are using (advanced fluid dynamics, advanced lighting, etc.) the more demanding the game will be.
If you wish to suggest a feature to be added to the asset, you can submit a request in the discord server under the 'feature-request' channel.
Yes the asset and the majority of its features have been tested to work on mobile devices.
If you still have any additional questions, ask them on the discord server here.