I use the Durablocks along with some others that are more rigid.
I even use a wood 2X4 piece.
the nice thing about the Durablocks and the wood ones is they are
so easy to true up.
Take some stick-on 80 grit paper and stick it
to a flat surface (like my countertop) and run the block
over it till it's even.
None of my blocks are that true when new.
the Durablocks sand easily and really show the low spots
If I want a really rigid Durablock, I can attach a piece of
plexiglass to it. Round the edges a little with sandpaper
to remove the sharp corners.