Privacy guarantees (or, rather, an explanation as to what you do with the statistics you can gather from people using the tile server) – currently it's not clear what's the policy for your site v.s. the API.

Plus, actually knowing about it in the first place would be nice! You have a piece of text saying "you don't need to credit us; just credit OpenStreetMap contributors because they made the thing", but it might be a good idea to say "but if you're feeling generous, you can tack a 'via NetToolKit' on the end". I found out about Mapbox, Leaflet and OpenStreetMap via those little copyright signs at the bottom of maps – and if asked, I'd certainly put one in for you if I were using your services.