Deutche Welle has a series call Nicos Weg, It is suitable for use with mobiles, tablets and PCs.
There are 4 levels but A1, A2 and B1 are useful for Rocket German.
Each level has many lessons with the emphasis on german comprehension but there is also grammar practice.
They could be used in various ways, but a good way is to do them after completing a level, so A1 after level 1 etc.
I did B1 after completing level 3 and found it challenging, but by taking it slowly and some use of a dictionary, I could get good scores. I have started on the A2 course and I wish I had done it earlier as there is plenty that I find useful.
All the instructions are in German which is a bit tough at A1 as the instructions are harder than the tests, but Google translate can help.