Hi! Been looking forward to this for a while. A few major issues I experienced:
The payment screen passes through an odd super detailed payment process which asks for extra details for the EU. I think this can be changed in the config. Unusually I was charged 20% VAT.
The demo tilesets aren't downloading from the downloads page (even in alternative mode). EDIT: Seems refreshing the page allowed the tiles to download.
The file browser uses a minimal version of the windows file browser which made it difficult to find the downloads folder.
I tried to open a file and I think I got the wrong type, causing nothing to happen (I expected at least an error!).
On closing the application it remained running, using 97% of my CPU.
There are a few kinks to work out before I can recommend this software. It seems like it's still in an early alpha state.