I must be in the minority here because I've never had major issues with ASUS products, though the caveat here is I have only used their motherboards. I'm using an x570-PLUS right now and it has been solid since purchase.
A lot of their shady practices are on their laptop side. For example their ROG laptops support USB PD as their main way of charging however asus forces you to use their own chargers. If you decide to use a third party USB PD charger (of the same wattage or greater mind you) then your laptop will disable the dedicated GPU and limits your fan speed profile to silent which causes your CPU to throttle under heavy load.
OLED Display on my Zenbook unglued itself after month of use.
They removed the ability to unlock bootloader in their phones (after repeatedly lying about it returning).
Some people sued them and won.
I won't buy another Asus product.
Same, my last 4 desktops since Sandy bridge were all Asus boards. Not that I'm not paying attention to all the issues people keep having with them lately