Not ready for public use.
CustomGPT has promise but it is nowhere near ready.
Buggy site and the underlying tech doesn't work yet. I was working with a large number of indexed sites, PDFs, Excel docs, and others. Ingestion seems fine but responses to prompts do not pull easy to find information in the documents, prompts must be very specific and even then only produce a response 10% of the time. The tool is also very slow at this time.
I'm hopeful this gets going but I'd advise folks to wait until CustomGPT gets their tooling working properly.
Also, lack of a free plan makes it difficult to try before you buy.