I have 2.5 lb round platemates -- they work fine with 15 and up dbs.
I'm using 5/8, 1.25 and 2.5 lb platemates... they do their job for transitions. I usually write down my weights in the terms of platemates, i.e. 8+5/8, 8+1.25 or 8+5/8+1.25, etc so I know exactly what I need to add on.