LVP and Underlayment Questions

[Adam Sharp]

What is the general consensus out there given the two options below:?

LVP with underlayment attached

OR

LVP with detached/seperate underlayment?

I'm leaning towards this combination for my condo project:

LifeProof LVP w/ Underlayment atop Quietwalk Underlayment

Is that overkill? Can anyone provide the tried and true most cost effective method? My rationale for going the route above is that I know as an amatuer I will only be able to get the floor "SO" level and this would give me the most room/cushion for error and hide more imperfections. Added benefit is it will stay warmer during Seattle winters. The manufacturer says NO underlayment with the LVP linked above (voids warranty) but is this a real concern?

Thanks!