Yes, there are major differences between the G1 and G3. I have both (unlac) for my ZUL tenor and ZUL alto. If they can't hear the difference between the V1 and these other two necks on the alto, why'd they make the alto neck in the first place?
It's simple - that's the difference I want on my tenor. Neither the G1 or the G3 on tenor does what the V1 does for their alto. Surely they can understand that, and if not, I'd be glad to send them some videos. Weird that they asked that!
The V1 not only takes the edge (highs) away, that are inherent in the G1, but it does so without creating the resistance that the G3 unquestionably has, or the blocky shape of sound the G3 can have in certain registers. Where the G3 seems to get its warmth while at the same time being subdued, the V1 is warm and focused, more like the traditional Selmer Mark VI sound. The G3 seems dark, where the V1 seems rounded, but not dark. The V1 still maintains a strong amount of punch and a very seductive shape of sound to my ear, moreso than the G3.