The last sidewinder I used had composite pallets. I quite liked them, certainly seemed as sturdy as ali pallets, lighter weight of course but nothing that would make me dislike them.
The only thing I didn't like about that particular press was the pallet arms suffered a bit of deflection under pressure. I'm not entirely sure what the "R" signified, but I understand the models with sideclamps had a longer pallet arm than those with back clamps. How much longer I'm not sure, and could well have contributed to the deflection I could feel from the model I used.
I'd probably buy one though if it was a bargain.