I used this for a team hackathon and it took way too much time to build understanding of the codebase, wrote too many agent transcripts and spent way too much token during generation. It also failed multiple times when either generating agent transcript or extracting things from agent transcript - once citing "The agent transcripts are too complex to extract from" - quite confounding considering it's the transcript you created.
For what we were trying to build - few small sets of features - using gsd was an overkill. The idea was to get some learnings whether gsd could be useful - for our case it was a strong no. Learning for me: don't overcomplicate - write better specs, use claude plan mode, iterate.