Getting better at playing the guitar is quite possible all on your lonesome, but this doesn't hold true when you want to learn to play the bass. Your other band members expect you to form a tight combination with the drummer. So that is what you are training for, as a bassist.
A metronome won't do (too mechanical; no feel), and your real drummer would rather play with you, than help you do your boring practice routines.
The Beat Buddy Mini doesn't feel mechanical, at all. It feels just human enough to help you practice, and is machine enough not to mind doing that for you ... at a very affordable price.