Generally sunglasses with clip on/magnetic ones the shape cannot be altered much. What do I mean by that is that, for example someone who's degree causes the lens to be more convex towards the center will cause the clip on to be "pushed" forward thus increasing the chance of the clip on to drop.
Custom made sunglasses-wise, you can request for a certain amount of curvature for the lens when you order the lens from the Lab so as to fit the frame better. Which equates to a better shape frame e.g the Temples/legs of the frame to be spread out too wide.
But clip on has it own benefits which of course is convenience of taking off when indoor or putting back when going outdoor.
UV protection is also the primary concern, I'm not too sure if the clip on/magnet sunglasses have their own uv protection but the lenses beneath the main frame should have the protection. Whereas custom made sunglasses, some lenses are done without the multi coat and thus doesn't come with the uv protection. Multicoating can be requested too however it might affect the coating process slightly.(take note uv protection is still the most impt).
TL,DR version is that both is sufficient but depends on your eye prescription degree and whether or not cost is an issue.
Hope this helps for now.
(Correct me if I am wrong)
