So I see zero, du, apus, uc browser, etc. All these free apps pushed around.
How can they offer 0.2-0.5$ per install? From what I gather so far it looks like they push a lot of ads/other app installs.
What are other monitization methods do they use?
If anyone can share resources/articles it'll be great
For legit apps, the business model is either freemium (pay for more features) or/and advertising.
For shady apps ... all sorts of nasty stuff.
I installed Zero Launcher a couple months ago to try and see how they monetize, and basically, I'd say their main source would be that the Play Store is relegated into a deep folder by default, and replaced on the front by their own "App Center", which I assume are all apps they push as affiliates or are their own 
Mehdi
This is an insane way to monetize!
I heard they could deliver up to few hundred K installs per day via their in-app promotion. I believe a lot of advertisers are willing to spend huge money to get that kind of installs per day!

Launchers do all types of tricky stuff like that. For example, when I try to open a PDF, they hide my default PDF programs and tell me to install Microsoft Office Mobile which is CPI for them. They make it all look like default android. They also install widgets which only purpose is to recommend another app they get paid CPI for.
I still love using Launchers though cause they are awesome.