Pressurised Pond Filters give you the benefit of allowing you to bury the filter below the ponds water level. This makes them extremely easy to hide.
Once water leaves the filter it can be moved practically anywhere by way of a hose as the water is always under pressure until it leaves the hose. You could for example have the hose outlet at the top of a waterfall whilst the filter itself is either buried or situated out of site in a garden shed. This type of installation would be impossible with a traditional gravity filter. The Gravity filter would need situating at the highest point as once water has left it then flows back to the pond by gravity.
Pressurised filters will need maintaining more frequently than the equivalent sized gravity filter because of their compact size. However this need not be too much of a chore as the better specified units such as the Fish Mate Powerclenz have knobs or switches to make cleaning simple.