Well I prefer boards of different widths and this is why:
The plastic squares just will not work in many cases where you need to level your trailer.
Twice recently I have been in State or National Parks where the only suitable site for my trailer was VERY un-level. In both cases I had to stack my boards 4 high, thats almost 8 inches of rise.
To get the trailer wheel up on those boards I had to use two of my longer 2x4s about 18" long, as ramps. this worked well.
This could NOT have been done with those plastic squares.
Additionally wood grips the ground surface much better than the plastic.
I carry about 10 pieces of wood of 2 different widths some are 2x8 and some are 2x4. This combination works great.
These are all short pieces so they fit snugly into a plastic organizer in my forward storage area.
The best part is the wood is very cheap as I get cut ends from the big Home stores for very little $$.