I have had both N. Caudopunctatus and N. Similis for about 1 yr now. They are in separate, species only tanks.
The N. Caudopunctatus would not use any shells I provided so I am using some rock piles and a breeding cave. They have spawned for me but I'm not sure whether they used the rocks or cave. I have not noticed any aggression with multiple males or toward the adolescent young.
The N. Similis are fanatical users of the shells I provided. They really like the whale eye shells. I initially purchase 6 and they are very prolific for me. I have multiple generations living together extremely well. I have not noticed any aggression with the males that resulted in any deaths or injuries. I do have a large Anubias 'Nana" and some rock piles to allow them to dash for cover if need be. I Will say that these fish are extremely entertaining and show attitude with their different personalities. They are always moving debris, snails, sand, etc. away from their territory. I did try adding some Ghost shrimp to help with cleanup chores but the Similis would NOT tolerate them at all. They became extremely aggressive so I removed the shrimp.
I forgot that I also have a group of Lepidolamprologus Hecqui (1M + 3F) that are big users of Muffin Snail shells. I have them in a 125G tank that, unfortunately, also has Aulonocara Peacocks in it so I have not been able to see their true personalities. I really need to remove the Peacocks and set this up as a strictly Tang. tank.
Lamprologus Ornatipinnis is also an avid shell user. I had a pair that spawned and the fry are growing well. Unfortunately, I lost the male last month so I'll be on the lookout for more of these fish.
I have purchased all these fish through my local fish club auctions, club member private sales, OCA Extravaganza or a local fish store that has very nice African cichlids for sale. I find the best deals are through my local club.