I got what we call a Navy style over here cause with limited scope you do rely on mass and a friend's sportboat has had good success with his 15lb Navy. This is what they look like (attachment) to translate the English
I don't have access to the Rocna anchors here in the states. But basically I have no issues anchoring in sand or mud or rock (the anchor snags or digs in). But gravel is like marbles underneath and I just drag along even with 8 :1 (or more) scope (e.g. a shallow site).
Obviously I am rarely using what a yachty would even consider an anchorage. I mean its a divesite afterall, not a 30ft deep sandy bottomed embayment, lol.
Based on some local suggestions I'm going to try a Danforth style and see how it works. 8 or 9 lbs is fairly oversized for the boat but managable for my arms. The extra mass will help for deeper sites when suitable scope is impossible to pay out. I do have a sentinal I can use for these too.
I figure the points on the Danforth might be able to insert themselves in between the gravel/stones like the Navy has been unable to. I have the benefit of always being able to check and/or reset it if I don't like how its laying on the bottom or just marginally snagged at a rocky site.
ps we do use a live boat with a vertical shot line for some sites. But I'd rather not arrange for a boat tender at a site where diving from an unattended boat is fine solely because I have a sucky anchor.