I haven't given that tool much of a try specifically, but overall I wanted to build something where you could do granular and flexible modeling across multiple scenarios in a modern and responsive UI, where you don't link your accounts, you control and experiment with a wide variety of options and assumptions, can plot/visualize what you want and see breakdowns of what happened in each simulated year, etc. If you check it out, I'd be particularly interested to hear what you think of the Milestone system, where you can define key events/stages in your life, add multiple criteria with conditional logic for when they should occur, and bind the start/end of other events in your plan to them (with support for offsets as well). So far, I haven't seen anyone else try to build that kind of system.
