I'll admit to buying and using a strut brace for the hell of it
However, strutbraces came from Rallying and suspension towers on them similar to the front of a k11 where they were angled.
However, in rallying the suspension takes a major beating so strut braces was used to keep the struts where they should be. Using them on a road car and on roads, makes next to no difference in handling (The only difference noticed is imagined in your head to warrant £40), they are also no use on a suspension where they are sat vertical and straight (such as the rear of a k11)
If you want to improve body roll and cornering, the best way to do it is to use better Anti-Roll Bars and to increase your chassis rigidity again the best way to do it is a full roll cage.