I've done a lot of soldering on RC stuff ranging from bigger gauge motor/ESC to the smaller airborne RX stuff. Personally I have never found a good use for those third hand gizmo's, although it may be an operator error. It takes some time to get everything orientated & even so its kind of suspended in mid air (or to the weak rigidity of the links). Sometimes the clamp strength on alligators can be excessive on the wire sheath. Sometimes the metal itself conducts heat away which may or may not affect soldering.
So my method is primitive but effective. Kapton tape & any kind of heat tolerant surface (glass plate or even certain grades of laminate are fine). I just tape the components or wiring down, usually with a single piece laterally so the joints are orientated. It takes like 2 seconds & end result is completely hands off because I usually need one hand for iron & the other for solder. The tape is meant for this kind of temp & the adhesive does not soften or leave a residue. The surface acts as a 'base' there is nowhere for the components to drift to during soldering once tacked down with tape. I could scare up some pictures from the vault but hopefully this provides food for thought.