To clarify Jay's statement, the JCW brace does not cause mushrooming in any way, but it does little to prevent it. I have one on my R53.
1. Vehicle type: R53
2. Mushrooming, torn strut mounts, or both: Both
3. Wheels/tires (e.g., 17" run flats): 18" run flats (3-season), 17" run flats (winter)
4. Any preventive measures (e.g., strut tower plates, braces, or camber plates - please describe make/model): CravenSpeed Under Tower Indurators
5. Have your preventive measures been successful in preventing mushrooming or damaged towers?: Yes on mushrooming, jury out on strut mounts
To be clear, I used to use the competing product to the CravenSpeed UTI (MINI Madness' Strut Tower Reinforcement Plates), but I found out the hard way that they are badly designed. The hole in the middle of the MINI Madness ones isn't large enough, and over bumps, the top of the strut mounts would hit them, causing the strut mounts to wear out VERY fast. I switched to the CravenSpeed ones only a few months ago, and I'm hoping that the strut mounts last a lot longer now. Both products have prevented any further mushrooming.
The main reason I have bought these products is because they allowed me to keep my JCW Strut Brace - since it's OEM and that's what I was going for. Ultimately, M7's Strut Re-Inforcement Plates or Strut Tower Brace (which includes the plates) is a superior solution, but then your JCW Strut Brace goes to waste (unless you resell it, I suppose).