I own a OnePlus 6 with postmarketOS. My daily driver is a Pixel 7 with CalyxOS and microg turned off.

Despite having effectively only FOSS apps on my Android daily driver, I can't daily drive postmarketOS. It's making great progress, but isn't nearly stable enough as a modern smartphone, and several other issues hold it back;

• Sleep states. Currently you get to choose between your phone going to sleep (~ a day battery life) but without notifications, incoming calls, alarms, etc. Or your phone "staying awake", where you'll have those features but only ~4 hours battery.
• Hardware video decoding, which "can work" but only in select apps, and they're not great for mobile.
• Audio issues, such as no audio from the earpiece, microphone not working, or no audio at all.

If you rely on non-foss Android apps, there is Waydroid, but it's not a perfect solution and might have issues.

It's not a "waste of money" if you want a device to experiment or tinker with, or if you want to follow progress of Linux mobile, but it is extremely unlikely to replace your daily driver.