Hi Josh. Thanks for reaching out to me. FormulaDesk is totally free at the moment - I'm just concentrating on growing the user-base and ironing out any bugs, improve performance etc. I do plan on releasing a 'Pro' version, or maybe even splitting it up into three or four smaller add-ins that are more targeted.
The best way to stay informed is to sign up to the newsletter, which I actually only use to send alerts when a new version is available. I'll also use this to announce a Pro version, when it arrives.
When installed, FormulaDesk performs a silent update check once a day and informs you if there's a newer version, however you obviously won't see this alert if you uninstall it, or if you don't open Excel for a few days. The best is still to subscribe to the newsletter.
You can subscribe on the download page: https://www.formuladesk.com/download
Please let me know how it goes, and if you have any suggestions or advice for improvements.