In theory, there's a slight negative of rippled vs flat, in that a tiny amount of the ground coffee sometimes gets stuck in the grooves. The difference this is actually going to make to your shot, though, probably zero unless you have the palate of a Q grader.
Features and Benefits:
• Calibrated to 30lb of pressure
• Self levelling ring ensures a level surface
• Sizes: 51mm/53.3mm/58.5mm
There are a wide range of tampers on the market, I think most people will find that something like this is perfect.
A consistent tamp pressure and a self leveller (which uses the rim of the basket to ensure a level tamp), just ensures that tamping is locked in as one of the variables, so it's not something that is changing from shot to shot.