I am considering converting from the paid Vitalist version, therefore I appreciate the ability to import the data through an XML file into Toodledo. However this process did not work for me. Kept failing to do file size.
I only succeeded by saving the XML file from Vitalist, opening it with Excel, allowing it to make the XML into a table. Then I manually cleaned the data -- removing completed tasks and, most importantly, removing duplicate lines, which I had many. (Data --> Filter --> advanced --> etc.)
I was then able to import this table as a CSV into Toodledo. The file started with 16,000 rows although I only had 1600 items included completeds. I only brought in 175 items. This took me well over an hour.