The term tracker blocker covers several different jobs: blocking ad and analytics trackers on websites, detecting email read-receipt trackers, or the opposite goal of tracking prices or your own time. Before installing anything, be clear on which kind of tracking you want to stop or start monitoring, since the extensions involved work very differently.
Blocking trackers on websites
A general tracker blocker sits between your browser and the sites you visit, filtering requests to known tracking and analytics domains before they load. Look for one that shows a count of blocked trackers per site, lets you allowlist sites you trust, and publishes what tracker lists it uses. Avoid extensions that ask for permission to read and change data on every website unless blocking is genuinely their only job.
Detecting email trackers
An email tracker extension, often called a mailtracker blocker, works inside Gmail or another webmail client to strip or flag tracking pixels that tell senders when you have opened a message. Check that it works with your specific email provider, only requests access to that site, and is transparent about whether it blocks pixels or just warns you about them.
Price and time trackers are a different tool
A price tracker extension, including an Amazon price tracker, watches a product page and alerts you when the price changes; it needs access to shopping sites, not tracker-blocking permissions. A time tracker chrome extension logs how long you spend on sites or in browser tabs for productivity, unrelated to blocking web trackers. Pick the category that matches what you actually want to happen.