Hi mate, you've asked the million dollar question
I've actually had a strut brace, under my stairs now, for about 4 years, and I've never got around to taking it downstairs and offering it up to the car!
Remind me on Friday and I'll actually try and do something about it and fit it this weekend!
Benefits are considered marginal, and adding too much at the front will always increase understeer, but I think something like the strut brace here will only stiffen the chassis, not the suspension, so should in theory improve geo control under load, not that I expect the shell flexes all that much anyway. Who knows!
I'll try it and report back for you