Finished rebuilding a 350 page website with Source it’s now published and am impressed with the result. I bought the Source + Addon pack when I found out Foundry 3 was no longer going to supported at short notice.
Initially I had to refer to the Source workbook a lot getting started but after a while got the hang of it. I like the ‘lightweight’ aspect of it if any Foundry users are looking for a new home I’d recommend Source.
Finally I haven’t tested this extensively but I have been running various pages through Google PageSpeed Insights to test the difference between Foundry and Source. I can confidently say there’s been a speed (Performance) boost and improvements in the other categories (accessibility, best practices & SEO).