Guix still isn't particularly blazing, but Guile is definitely not the bottle neck these days. Guile is actually a very fast Scheme implementation now. The problem with Guix's speed right now is that the binary substitute servers have slow networking, so your options end up being either to compile software from source, or crawl through a slow download.
This is only usually a problem if you want to download something large or do a large update though. If you're just downloading a small program or you update your system frequently, it's quite reasonable to use.
As far as the "stop sign", I have never really run into that with Guix, and I did run into that with Nix. The fact that Scheme - unlike the Nix language - is not purely functional, I think encourages users to do what they want, even if it goes against the spirit of the functional package manager.
