I assume these are the pavers you are talking about.
I have used similar pavers from Belgard and Techo with great results. If price says anything then Unilock products are "better." They are very pricey up here. I would kill for 7 pallets at $50 per pallet. That pallet would run around $600 here.
I try to seal most of my installs but I have found that mildew and grim is due to where the pavers are installed and lack of maintenance. Blowing/sweeping/hosing off.