I haven’t, but admittedly, I haven’t had high usage. I’ve used it more for personal use. It seems pretty good at caching images though, so if the data doesn’t change often, you might be able to get away with not bumping into limits.
I’m not sure how reliable this link is, but it indicates that there is a 20,000 chart limit on the free tier.
http://54.90.241.242/pricing