[rogansage]

Building free tools alone is not a viable LT strategy, you need to market any tool (even the free ones) to get traction and usage. If you rely on SEO, you need to clearly demonstrate to Google that this is the best page for a search query (or set of) -- this is't very obvious to google if the value is not textual so this needs to be worked on to complement it (then you need backlinks too... the marathon begins).

I would question whether the 'ad-free' element of the strategy is potentially only a very small and ultimately insignificant weight in the perceived value of your tool vs others and might not be as impactful as you'd think -- if you deliver enough value for people not to care about having to ignore ads (which ppl are very, very good at these days) then they will confidently ignore the ads and find the value (e.g. academic referencing tools, wetransfer, {filetype}-to-{filetype} convertors)