If the built in 'mic' on your phone/tablet sounds better than when you try to use the pickup .. that's probably telling you something.

My guess is if the recording in RB used the pickup .. and the other devices just used their native sound input (built in mic), and sounded better .. either the pickup is the issue, or you don't have a good preamp to boost the pickup sound properly.
That's at least three of us now now pretty much saying the same thing.
It's likely the pickup that is the issue.

A pickup like that needs a preamp (it has very low volume/power on its own).
Feeding that level signal to a built in computer mic input is usually a mismatch, resulting in feeble results.
Just my experience.

A basic Focusrite unit would likely make things much better.
If it doesn't make the pickup sound better (and it likely will), it will allow you the option to mic the thing and get a decent sound.

I do not work here, but the benefits are still awesome
Make your sound your own!