I got so far with it. I didn’t get it working as a properly installed wordpress plugin, but I was able to get it to upload files nonetheless.
I installed it to the root of my web domain (as per their instructions) and I call it using raw PHP/SCRIPT from my WordPress page (using the rawhtml plugin).
I’ve had to move onto something else for now, but I will come back to it.
I did also initially have problems uploading the files, but that was down to a permissions issue on the sever. The upload directory needs to be owned by your webserver user (apache?), and needs to have 755 permissions.