I have been using the Gamikatsu Octopus 5/0 for casting eels for the last few years. They are less expensive then the Diiachi and when new nearly as sharp. The Diiachi is one of the most superior hooks IMO but I go thru a lot of hooks so I generally use the Gamikatsus. I use to use a 5/0 SS mustads but the Gamikatsu's and Diiachi are really sharp and pretty darn strong.
As far as circles go...if you are boat or bottom fishing and your rod is in a rod holder or sand spike...this are fine. I prefer the conventional hooks when casting eels. But if you modify your hook-set style I see no reason you could not use these as well for casting.
If I deep hook a small fish I cut off the leader. The hook will rust out pretty quick if it is not stainless. If the fish are small and this becomes a regular thing... I set the hook a little sooner.
I did not loose too many fish and had to take only about 4 or 5 fish home that would not have made it. (that is a low percentage)
I don't think any fisherman should rip the hook out of a gut hooked fish. The fish is better off with a hook in there that will rust out in a week. I also tried a cool hook remover that grabs onto the hook and when you sqeeze the handle the hook flips 180 degrees and you can extract it a lot more easily.
I will be doing more boat fishing next season
and I will be using more circles.