I am using Beatstep on ipad, I have the transpose working by using Akai LPK 25, it has a latch function and costs about £30, all you need to do is route midi out from LPK to midi in (via USB) on Beatstep.
To understand the transpose combinations the following rule of thumb will help.
If you always program your sequence in a key of C, it will always get transposed to whatever is the lowest note you are playing in your sequencer track.