Pros of Topmounts
What is the advantage of having a topmount?
JW Topmounting a longboard is the most classic mounting style that holds tons of beneficial aspects in comparison to other mounting styles. It has the highest ride height of any longboard, giving you the tippiest ride, and most turn possible. If you're looking for a nimble cruiser, look at a smaller topmount like the 34" Black Dog Butterfly.
Length plays a major part in the way a board feels, and so does the wheelbase. The longer the deck is and the longer the wheelbase, the flowier, longer turns your setup will make. If immediate response and quick turns are what you want, get a smaller board, or at least a board with a lot of wheelbase options, such as a Moonshine Rum Runner.
But if cruising, making big carves, and generally chilling is what you want to do, a Landyachtz Pinner, in all 44 inches of its glory, will be like floating on a cloud made of fun.
Downhill with a topmount?
Going fast on a topmount has many technical advantages, being the extra grip and maneuverability, but they are also the least stable of all potential mounting styles. This is due to the ride height, and the severity of quick-turning that comes with topmounts. So, if it's your first time setting one up, compensate with your truck setup being a lower degree, like 44 Degree Calibers to ensure a package that is more user friendly to a first time topmount rider.
Along with that, keep wheelbase in mind. If you're new to topmounts, maybe don't go right into a 22 inch wheelbase. Otherwise, you will more grip and turn then you are used to.