We don't truly know about overkill unless we discuss wattage and also "Why 6 volts?".
1) Why 6 volts? - one reason: 2x 3.0 volt cells. Easy dual battery
mod... no regulator required. You follow battery voltage.
2) You can still adjust the ohms getting a lower wattage if you wish.
So it's also a hardware/preference/PV design issue. Personally... I stay at a regulated 5 volts. Very consistent performance and plenty of "oomph" for the atty (3.0 ohm). But I suppose a 2x 3.0 volt unregulated mod is appealing to some... for mechanical mods that stack
batteries for example (prodigy).
If it's too hot.. up the ohms.
As with most things e-cig... to each their own.
Best guesses, 2 cents.
EDIT: The prodigy is a solid unit. All mechanical mods have less to go wrong with them. You have to play with atty ohms tho..... vv units or regulated units are nice, but have circuits that can fail. So it's kinda 50/50. Once you get the ohms strait... I think you will love the prodigy.