Actually, I tested three of them, to be precise, but one probably couldn't stand alone as a healing addon, and is more a raid frame replacement. Those three addons are Healium, Clique and Grid. I began with Healium, for no other reason than because that was the first one I decided to switch on, but as it happens that worked out pretty well for the testing as, when I wandered into the settings, I discovered it could work with Clique.
Healium takes quite a different approach to the other addons I've reviewed so far in this set of Addon Spotlights. VuhDo, Healbot, and Grid+Clique are all click-to-heal addons, that is to say, they take a set of either their own frames or a third-party set of frames, and set up mouseover macros on them. A left-click on a frame fires one heal at that player, while an ALT+ left click fires a different one. Healium, on the other hand, as can be seen in the header image, doesn't perform quite like this.