Update: also finding the beat sequencer included in the iOS GarageBand app really useful for practicing rhythm. Its much more dynamic / progammable than (most) metronomes, and provides an easy visual reference as to where you are.

For example: revisiting some of the trickier rhythms in Rock Level 2, I've now created a few beat sequences based on the notation in the lesson which I then practice along to. As I get something under my fingers, I tend to change to keeping my own count over a simple beat.

It's quite useful for messing around visually to create new rhythms to try out and practice.