I've built with GSD, and experimented with rolling my own. I think GSD is good if you don't know exactly what you want to build, but you only have a vague idea. However, if the opposite is true (and I believe it should be), then GSD has a lot of overhead, and costs a lot of tokens. Subjectively, my GSD apps looked very much like AI slop (the app itself, not the code), and felt soulless.