Just tried GSD and Plan Mode on the same exact task (prompt in an MD file). Plan Mode had a plan and then base implementation in twenty minutes. GSD ran for hours to achieve the same thing.

I reviewed the code from both and the GSD code was definitely written with the rest of the project and possibilities in mind, while the Claude Plan was just enough for the MVP.

I can see both having their pros and cons depending on your workflow and size of the task.