The Diamondback is a D-frame, but it has an extra thick topstrap and adjustable rear sight, which make it too large to fit most holsters made for other D-frame guns, but too small for many of those made for S&W's K-frame. Also there can be complications if the rig has a thumb break safety strap.
Having used them for numerous decades, I have no problems with holsters that fully expose the trigger guards on double-action revolvers. On the other hand, single-action pistols that are carried cocked & locked, and the safety lock (manual safety) can be wiped off are another matter.