A free download and unrestricted access are different things.
Start with logging
Use a routine and record the sets you complete. Compare this basic workflow with the requirements of your own training rather than choosing solely by a free label.
Check the review window
Premium adds full workout history and additional statistics. Inspect your installed version for the history and chart ranges available without a purchase.
Keep records portable
The released listing documents PDF and CSV export. Inspect an exported file before depending on it for an analysis workflow; export does not imply import compatibility.