I first tested this mod in the cubic shapes and it looked really nice although it was a bit annoying to build a roof for my house :] But I still managed to build the roof. Then I tested it with rough and liked how it looked more realistic. Finally I tested smooth and oh my gosh it looks nice!!! However loading the game and logging out of the game takes ages and loading map chunks is a bit annoying. So if you want slopes and if you're fine with map chunks taking 10 seconds to load and logging in or out taking a while then this is the mod for you. I reccomand it :)
Logging out takes some time because it waits all mapchunks to be generated before closing the (local) server, and natural slopes can be expensive on that side. If you find the map generation taking too much time, you may try the Progressive generation method instead of VoxelManip in the mod settings. It will release raw chunks faster and generate the slopes in background while you play (and you can enjoy watching it happening in front of your eyes :) ). But it will be even longer when you logout because the progressive method is slower in absolute time.
Once you start playing in already generated areas, the logout issue won't happen anymore. There are other parameters to tweak for performances against the number of slopes, but the generation method is the most effective without affecting the results.