R exsul is interesting because they lack blue spangling on the body, unlike the others in their Genus. They stick out for that, with just the dorsal lighting up.
I would like to keep that fish, and also to keep a Hemichromis one day. They are smart Cichlids, and fun to watch. If your tank is big enough, their territoriality calms down, but very few of us have the needed tank sizes at hand. I've had lots of chances at Hemichromis, and have kept a number of different Rubricatochromis, all of which were probably guttatus. We recently have been talking here about misidentifications with scissortail Rasbora, but nothing approaches the confusion you hit with Rubricatochromis.
I love Cichlids. There are no hard and fast rules for the group, and the diversity is awe inspiring.