It would be nice to hear from someone thats actually had one fitted to voice an honest view on both advantages and disadvantages of having a brace fitted.
From what i can work out, a brace between struts should should slightly improve cornering by reducing flex in the chassis allowing a more equal amount of force on all four wheels at one time. As flex is reduced this should help keep your suspension geometry level, giving maybe a firm/tight feel through bends. (this is only my own conclusion btw)
The disadvantages (as far as i can work out) becuase of the lack of flex in the chassis the force will be looking to give way somewhere else, which will prob be your tyres - resulting in loss of grip and spinning you out into a tree or something at next to little notice... Of course you shouldnt be driving to that degree on public roads anyway - but for the poeple that do they will sense a feel of understeer! With a brace my worries are you will not feel your limits until its too late!
again this is only what i think - if someone with an actual brace fitted could confirm it would be appreciated!