You can see the opponent's pieces in Fog of War Chess

It's the easiest 

And i cant abuse it due to how lazy I am to browse through inspect code 

how do cheaters use it?

Oh man, good catch.
Looks like they've fixed this @whatisupbub1 since then, I went and checked it out.

It is cleary true. When I have a "spectator", I loose most of the time (my rating is 1980). Each move is slow (10..15 seconds) even the most obvious of it. The anticipation was unreal after analysis. Very frustrating !

@Wibee2001 Could you share a link to one of your games where you believe your opponent was cheating by getting vision of the full board?
In my 6,000+ Fog of War games I have only encountered players cheating in this manner a few times. (I'm top 10 player currently rated 2270.) It's usually easy to analyze the players games afterwards to see if their play is suspicious. There's a big difference in the moves made between beginners playing with full information vs strong players playing fairly. Would be happy to take a look.

for me I can see the board normally and there is no fog