A broad knife is the preferred tool for hide working, and so this tool provides a greater benefit than other knives of the same quality. I'd expect the difference to be approximately one quality level, so a Masterworks knife of a different kind being about equal to a Fine broad knife.
You can experiment by having both a Masterworks "other" knife and a Fine broad knife in your inventory when skinning a carcass, observe the text to see which one the game selects, drop and pick the knives up such that they end up in the reverse order in your inventory, and then observe which one is selected for another skinning task. If the same knife is selected in both tasks that's the "better" one, and different ones are used they're equally good.
If I remember correctly, a Fine broad knife is sufficient to be able to make Superior hides, while a Fine knife of other types fails the equipment test. However, I may remember incorrectly and that's for Decent knives, but anyway, a Broad knife can be of one quality level lower than other types to allow for the same best result.
Thus, I'd expect a Masterworks broad knife to add an extra bonus to your success roll over a Fine one, which matters a fair bit when the chances are so low.