These add ons may not work as you expect. They do not scrape your browser session on Amazon to keep track of prices.
They just ask Amazon for the prices. It's Amazon's price history.
Has anyone mentioned that a lot of "instant coupons" are now being used to hide price history?
Anyone using these services notice how every single item on Amazon got listed suddenly brand new about a year ago?
Maybe don't trust the merchants to tell you the true prices of things.
Incidentally, neither service especially hides this. It's on you if you think they're keeping track of in vitro market prices.