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The diamond might be similar to the feather blades giving a slight harsh edge for the first couple shaves. Stropping the heck out of it will help so try the diamond with a really good strop session...

Maybe a good question then is what type of blade d you like. Really sharp and keen, slightly more mellow and a bit softer? What type of edge do you want.

Don't need to but it's personal preference. Some prefer the crisp edges left by diamond. Others dont and will use crox to smooth the edge to a greater comfort level.