Is it reliable?

Does 4G LTE work?

Does the mobile hotspot work?

Is texting reliable?

Yes, it's essentially as robust as stock Android.

Occasionally, there are issues with a new feature not caught during testing that are fixed promptly by a new release but the same thing can be said about stock Android.

Does it cause weird battery drain?

No.

Can I install any app from the play store just like any other Android device?

It bundles the F-Droid app store, and the Yalp Store app from there can be used to install apps from the Play Store. However, it doesn't include Play Services and many apps from the Play Store depend on it for some of their functionality or in some cases cannot function without it. Those apps could implement alternatives when it's unavailable but most don't bother. Some apps like WhatsApp use Play Services when available but work perfectly well without it too (at least after adding a battery optimization exception in the case of WhatsApp, which it should explicitly request from the user).