The Drain holes are standard on all of the AIRE floors, although they do make a sealed floor as an option (not for Tributary). The sealed floor is the same only it does not have the drain holes and it has waterproof zippers. The boat stays lighter and surfs better without any water in it. Probably a waste of money unless you are creeking with the raft (puma). The tributaries are made very well, you are saving your money mostly in cheaper material and valves and sacrificing your great AIRE warranty.
Most of the Tributaries can be a challange to design a good frame for because they have small tubes and the floors rise very gradually That means finding a good spot for your cooler is a challange, and don't expect a big dry box.
If you plan on keeping the boat for a long time, consider an AIRE instead.
My 2 cents