Starting with the GOOD.
 
x12
Love the light feel of the mouse. Shape is good too. Wiring seems ok and is very light.
 
x15
Love the build quality feel. Everything feels like the components are higher end. Button locations are good in my opinion.
 
The horrible:
x12
Not being able to turn off the buttons on the right hand side is just torture. In a game every time i lift the mouse one of the buttons if pressed. Very annoying. If I tore them out will the mouse still function? Anyone try this. Or any ideas? For 15 bucks I don't really care about the warranty. 
 
x15
The shape of the mouse is just plain bad. Almost impossible to lift the mouse due to its shape. This right here makes the mouse unusable for me. Instead of having the shape be a pyramid, it should be v shaped.
 
 Update:
Did some tinkering and solved the problem with x12. First I tried to gently remove the buttons. This did not work because they are on there pretty good. So I found some non slip pads for a computer case that I had laying around. I attached them right under the buttons and this prevented the inadvertent button presses. Something like non slip pads that are under the keyboard should work as well. Going to do this with the x15 as well. Should help with the grip.
 
 

Was going to upload an image of Unleash RGB setting the button to disabled, but the image gets scrubbed, as it should, but turned into text.
Anyway, cannot you just set the button to disabled?

It's not the most amazing software. Just be sure to go in the settings and disable the start with OS option. Only open and use it when you want to change the button mappings and whatnot.