They fill different needs. Feeldoe, Nexus, Sysil:Edge, Share all have different strengths and weaknesses. The Vixen does work very well with a harness, because the "joining plate" gives it a lot of stability. The Feeldoe and Share are probably the easiest to hold in without a harness. The Sysil:Edge has some features that give it more stimulation than you expect from its size, but the giver's end is a bit harder to hold in than some of the others. The Nexus and Share are the softer models, so they're best if you're interested in using them in many different positions.
My video review is in the editing stage, but I literally have over an hour of footage I'm trying to condense down!