As I said before, the choice of sgian dubh is really entirely personal. Some are obviously more formal than others, but as a general rule you can wear just about any style of sgian dubh to formal events, but formal sgians dubh should not be worn casually.

I have one of the classic "dress" sgians with a stone in the cap, and my clan crest on it, that I wear for formal events. I also have an officer sgian dubh as you describe that I wear every day. Then I have one made up from a Victorian by-knife that I like to wear for special events. It's an antique, so it doesn't get a lot of use.

I used to have a relatively plain one, oxhorn, carved into a thistle, that I wore for all occasions, dress or otherwise.

Point is, it's entirely your choice!
M