(sorry if this has been mentioned before)
I'm not sure if the Skritter vocab database includes a measure word field, but I think a measure word practice option / mode would be very useful.
I'm imagining something like a prompt with e.g. "一 ... 人" and a voice reading that where possible, and the user might write 个 or 位 in this case.
The prompt could then display "一个人", and maybe the voice could even read it out for extra reinforcement.
I imagine the basic means for this would already be entirely possible with Skritter's existing technology, and would be extremely useful for most users.