As someone who uses sound apps for typing I think this is a great idea.
Couple of things though:
There should really be a volume slider for the typing noise - if a person needs to turn down their computer volume to control the sound but then can't hear their Spotify properly it can become a problem.
When changing the theme from espresso or skateboard, the font changes back to nunito and you have to select another font then select the one you had again. Small problem, small fix probably.
Obviously it'd be nice to have a larger selection of sounds. If you want anything custom recorded I'd be happy to help out as I'm a sound designer. I won't charge, seeing as you've provided the app free of charge as well. Plus it'll only take me a day or two to get it done, even if I'm being lazy lol.
Keep up the good work!