I'm fairly certain this is in the article:
For trading I recommend Kite, mainly for their stable Connect APIs and the low bandwidth. Their limitation is 3 requests per second, and this was more than enough for my new strategy. Getting solid historical financial data isn't cheap, and with so many people hitting the providers to scrape and download data, I don't blame them for limiting the offered information. Intrinio is a good provider for real-time stock quotes at very inexpensive prices. However, getting access to more in-depth data would always yield better results.
I talked about it in the interview. For this first version I used Kite for trading and mostly Intrinio for financial data. Costs vary from provider to provider, but for testing this, I went with some of the least expensive ones.