I am of the considered opinion that GSDevTools is one of the best things since sliced corn-bread!
However ... I occasionally (and increasingly) miss the ability to manually step forwards and backwards in the timeline. I recognise that GSAP is not frame based, but in this context of stepping - I would love for it to behave as if it was. i.e. Hit the step-forward button (key) and the timeline advances +1/24 of a second.
I figure there could be a default notion of 24fps, but that could be overridden with an optional named parameter during tool creation. And maybe even an option to snap to the absolute frame during step (like snap to grid).