Yes, often, if you still debug individual URLs in anger. No, not as your only system, if you sold ongoing portfolio care.
Keep GTmetrix when
You need observed Chrome behaviour, a clear waterfall, or a test from a location that matches a regional complaint. Your developers already think in GTmetrix filmstrips. A client dispute needs a specialist artefact, not another lab card from the monitoring tool they already ignore.
Add monitoring when
You manage many client hosts, you cannot remember who last ran a check, or your monthly review starts with scavenging screenshots. You need Viewer access for clients without sharing an admin login. You want budgets and alerts tied to dates rather than heroic memory.
A sane stack
Scheduled monitoring for the pinned money pages. GTmetrix or WebPageTest for incidents and launches. PageSpeed Insights when you need a quick public link. DebugBear-class monitors if you already bought continuous CWV elsewhere. Apogee Watcher is built for the schedule layer, not as a claim that real-browser diagnostics died. “GTmetrix alternative” in search often means “I need the next operating model,” not “delete every diagnostic bookmark.”