Flattening paint is done by adding silica to the paint and it will disturb the surface as the solvents evaporate. The solvents are usually water in acrylics (urethanes usually) at first and then lesser amounts of hydrocarbons... point in the description, the surface is rough and will wear quickly making it a poor sealant. For serious sealing always use gloss and roughen the surface.
On the other hand, the stock probably does not need it.
