Just catching up on this thread and honestly, I feel your pain. When I was finishing my kitchen last year I went through the same thing with a stand mixer. Prices are basically a rollercoaster. In my experience, the safest way is using tools that dont require any login info at all. Over the years, I have narrowed it down:

• CamelCamelCamel: This is the old reliable. You just paste the Amazon link and tell it what price you want. It emails you when it hits that mark. No password needed.
• Keepa: It has way more data, but honestly might be too techy and cluttered for what you need. I would go with the camel site for your fryer. It is the most conservative option and wont mess with your privacy. Just stay patient, that price will dip back down... it always does.

To add to the point above: I totally agree about being careful with extensions. I once installed a tracker that kept asking for permissions I didnt like, so I wiped it immediately and went back to basics. Safety is huge for me when I am shopping online. I mostly use Keepa now because the data feels more solid, even if the charts look a bit intimidating at first. It really helps you see if that $115 price was a regular thing or just a one-day flash sale. Quick tip: keep an eye on the Amazon Warehouse listings for that Ninja. I got my blender that way and it was basically brand new, just had a dented box, and it saved me like forty bucks. If you are trying to coordinate with your sister on which model to get, Cart to Link is pretty handy for sharing your basket as a single link. It keeps things simple and you dont have to worry about sharing account details or anything sketchy like that.

I am honestly so happy someone finally brought this up because i have been dealing with the exact same headache for like two months now. It is so frustrating trying to buy gear for my place when the prices jump around every single hour and i just cant find a tool that feels 100 percent reliable. I even tried checking out this Chrome extension but i am still totally stuck and worried about the security side of things just like you are. Ngl it is kind of a relief to see others struggling with this too because i was starting to think i was just bad at using the internet... hopefully we can both find a safe way to track these prices soon.

Stumbled upon this today and happy to chime in because I have spent way too much time tracking gear for my own kitchen. To add to the point above: Camel is solid, but you gotta be careful with some of the newer browser extensions that pop up lately. Before I give you my full setup though, which specific Ninja model are you looking at? Some of them have exclusive prime deals that track differently than the standard listings, so it helps to know if its a special SKU or a bundle. A few things to watch out for:

• Never, ever give a third-party app your Amazon password. Any tool worth using only needs the URL or an email address for alerts. If it asks for login, its a huge red flag.
• Be wary of deal sites that make you install software that tracks your browsing history. Stick to the web-based ones first.
• Sometimes these trackers miss lightning deals because they happen so fast... gotta keep that in mind. I have been using carttolink.com lately to share my lists with my sister so we dont buy the same thing twice when stuff goes on sale, works well and no complaints. Honestly, once you get the hang of price history graphs, you will never pay full price again.