If you lurk around Indie Hackers or Hacker News for a while you'll get the impression that Google Alerts is the most popular keyword monitoring tool. Everybody knows about it, everybody tried it. It may therefore come as a surprise that Google Alerts doesn't really work. For an indepth explanation see the excellent write-up Google Alerts: How it Works And Why It Doesn't.
In short, Google Alerts will:
|Free||Pricing||Free and paid|
|Simple filters||Filtering||Advanced filters|
|Undisclosed, but possibly the whole Internet||Sources||A few select communities|
|Misses results by design. Significant false positives||Accuracy||As precise and complete as possible|
|Email and RSS||Notifications||Email, RSS, Slack and API|
Because they are free and crawl the whole internet, it definitely won't hurt to set up Google Alerts for your keywords.
Use Syften if you want advanced filters and don't want to miss results.