^^^^
The one point against the complete frontal undertray is that it will conceal any fluid leaks until they become far worse.
On the floor of my car's batcave (garage without electricity) I keep pristine brown cardboard under the whole area of the engine. Consequently I can immediately spot any drops of fluid. I caught a faulty DSG oil plug seal that way and before it became a serious problem.
In the UK, unfortunately without unrestricted speed autobahns, I don't consider the underfloor aerodynamics of a VW Golf hatchback to be that important.
I think that you are something of an expert on the aerodynamics of the Golf and so I am very interested in your thoughts about the UNIbrace UB regarding underfloor drag etc.
Also whether a Golf which is lower on suspension has any aerodynamic underfloor advantages or disadvantages
(Mine has 95mm overall ground clearance)