Comment by wolco2

Beware building against a paid api as the rates/rules will change under you and you will be more stuck compared to a public api.

I wouldn't trust any api you don't control, don't have a solid contract (without the changable terms) or isn't owned by a nonprofit.

The free ones will hurt you but you expect it. The paid ones hurt more because you often build a business around an ecosystem that eats you up.