While I am not familiar with this particular extension there are a lot of price comparison sites and they work on the basis of referral fees–so only include sites which provide these fees. Thus are not comprehensive.
I happened to watch that video (it’s becoming very popular for some reason ).
This got me thinking about how useless sites like retailmenot have become. Non-working codes, and a lot of clicks just take you to the store site. No doubt to get the affiliate fee but no attempt to produce a discount code.
Plus if you Google for coupon code sites you just see a zillion copies of the same basic sites.
If Honey/PayPal was a legit outfit it would also have just a plain but actually useful website for code searches that you would bookmark.