I have built and modified many cabinets and in general the function of the rails is very dependent on how exactly the cabinets were made. The vertical panels to which the fixed elements of the rails are attached must be parallel to each other and properly spaced. In my opinion, bottom rails generally work better and are easier to install than side rails, but they're also expensive. So if cost is a critical issue, side mounts are the way to go. Compared to other soft close side mount rails I have used these work better and the price is attractive. It is very important to measure the distance between the mounting points and the spacers to ensure the rails are parallel when assembled. The damping mechanism has a limited closing force. If the rails are not aligned and you add the weight of the box to the contents, the retraction mechanism will not be able to do its job.