I've used
block.io on many occasions over the past couple years, and have never had any problems with them. (Not affiliated in any way, just a happy user.)
The API is ridiculously easy.
https://block.io/docs/basicBunch of simple GET requests. (Assuming you don't opt for one of their libraries, and stick with the RESTful service.)
For bitcoin, I recall the permitted TX fees as being a bit steep. But the wallet also has Doge, and Litecoin, so you've definitely got options.
I personally haven't hit the limit, but you're only allowed 100 addresses per network, (They let you run testnets!
). So that could be a problem if you're looking to accept payments with them.
Or. You could also cough up 100 dollars a month for extra features. But I'm not doing that.
As to whether or not they'll end up scamming, that's anyone's guess...
But they've lasted a long time so far, and I've never been given any reason to doubt them.