I have K451LN. Everything is good enough for the price (good viewing angle, good battery, good looks, good idle noise), except for the keyboard. It's not so nice to type on. Very often the spacebar or left Shift key does not register. Took some time for me to get used to hitting properly. My last laptop was Acer TimelineX 4820TG. That keyboard was better.

Another not so good thing is 4GB RAM is not enough for my Chrome usage.

One thing you need to do right away is to disable or uninstall the "splendid video utility" by ASUS. The display colour is so inaccurate with that. After that just use the Adobe RGB profile. Then the white will look more like white. Go to http://www.lagom.nl/lcd-test/ if you don't know what I mean.

I went to check out the same model again, and I found out that the keyboard in my model is unusual. It should be nice to type. So with that out of the way, it is a good bang for buck IMO.

Heat dissipation is good. I leave it without laptop cooler on my desk 24/7 (almost) and it stays cool. When I play The Sims 4, the right area of the keyboard feels warmer over time, but the bottom doesn't change. So it's really cool (pun intended).

K451LN is 14". K551LN is 15".

My laptop is on 24/7 and the back is still cool. Not sure about long term though. Still, better than my previous laptop.

Teamviewer in from work, overnight torrenting, or Spotify to sleep.

The 1tb HDD gave way. Failed short drive self test on seatools. Event viewer constantly showing bad block error. Didn't register laptop for warranty (ignoring the Asus registration popup all the while). Can't afford to wait for warranty, so bought an ssd to replace. Upgraded to windows 10. Atk driver from Asus support website works. Now avoiding running 24/7. Back to business again.