I can't speak to the VW Monster mats either, but the OEM Audi TT cargo liner I got (too niche a vehicle for WeatherTech to bother?) surprisingly is not as nice a material formulation as you get with WeatherTech, although it does fit perfectly.
I'll go with the Monster if available upon ID.4 delivery tho', just because.
I have the same VW Monster Mats in my 2012 CC that I drove off the lot with in September 2011. I'm very pleased. I am equally impressed with the WeatherTech floor liners in my daughter's 2014 Honda Civic. Both are great options. I would lean towards the VW mats for the ID.4 insignia.
You remove the stock thin carpeted mats when you install either the Monster or Weathertech.
In the front foot wells you would have no way to use the pop-pins to secure them in place. Securing them in place is important in any vehicle as it's possible, albeit rare, that the driver's side mat could slide forward and interfere with accelerator/brake pedal function.