It would be nice if there were other mechanisms to get you the answers we need more timely, but this tool is used as is with little instruction. Best hope is for people that have used this be nice enough to provide input.
I've used this tool to migrate reports 2005 to 2012. It was a little frustrating at first because my subscriptions were not transferring. In reviewing the log file generated by this process I really paid attention to the errors. Although you'll not see "your subscriptions didn't generate because", resolving those errors is key. You may still receive errors that the parameter is not supplied and for any .rdl error your subscription for that report more than likely won't generate.
Bottom line: after you select your options on the report tab, to include subscriptions and choose your location and script your objects; open the file and simply change the URL to point to your new server ....
In the folder(s) that contain you actual .rdl and .rss, you'll need to open all .rss file and provide passwords for those that have passwords required for them. In my case we used dynamic connections which required passwords for each .rdl file.
Very important: Open your Data Sources folder and for each .rss file open and provide the passwords for your connections. This will allow your subscriptions to generate. This took me a while to catch.