There will always be wasted paint even though it may be the tiniest amount irrispective of the type or size of cup, paint by nature will cling to the sides and bottom of the cup so it's impossible to syphon out every single drop, if this was possible there would be no need for cleaning
It hasn't been mentioned yet and I forgot to mention it too but the bottom of the original iwata/olympos side cups are removable for easy cleaning, this isn't possible with the aztec plastic ones, in all cases you don't need to make any modifications or add anything to make them fit.
Yeah I know, but I'm guessing for the suction there will be more unused paint than the gravity feed ver. I dunno bout the side cup ver.