I would get the nano wavebox, in a smaller tank like a 120 the wavebox doesn't add enough increase in waveheight to justify the added expense and bulk, a 6212 if perfectly tuned on a 4ft tank may give you a 1/4- 1/2" bigger wave, the 6206 will do an 1" wave for sure and it is easier to tune for smaller tanks as the pulse frequency of the controller is biased toward pulsing faster for smaller tanks.