It's a self-updating hosts file. If you only do it once in a month you'll start seeing ads again. Also you can edit the hosts file if you're rooted, but you definitely can't if you're running a stock unmodified ROM. If you're rooted and you only care about your Android phone, you can also install Adaway, which does pretty much the same thing without the whitelist capability (Get it on F-Droid), but if you have a number of devices to protect, and some of them are iOS devices, TVs or whatever that can't be rooted, jailbroken, or you don't have administrative privileges to, Pi-hole is a good choice (if you run pfSense at home you can also use pfBlockerNG, which is essentially the same thing too).

Host file blocking on mobile devices produces some weird web browsing. I like using browser plugins because it gets rid of the whole chunk of html so it's like the ad was never there in the first place. On android, there are these huge blank spots you have to scroll past to keep reading. I still keep adaway on but I wish I could just use ublock origin with android's chrome.

You can use uBlock Origin in Firefox on Android, and I've found DNS66 to be a good non-rooted adblocker on Android.

Now there's also Blokada which is a little bit better (found it to block some ads that DNS66 actually let through; it was a random discovery, I am not a researcher).