Not sure what the problem was with the download but it seems to be working fine now.
On the differences between toolkit and ISA... here's a short and incomplete list:
- In ISA no need to add your files, works on the active project/file
- In ISA no ability to perform actions across projects
- Toolkit has a much more powerful set of search & replace features
- Toolkit can split files
- Toolkit uses boolean logic to select segments with specific TM match values so potentially more powerful
- ISA makes selecting segments with specific TM match values a piece of cake!
Then there are a few small differences here and there. I think the intention of the ISA plugin was to make it easier and more integrated to do the most common functions in the toolkit. Horses for courses I think!