The only time I have noticed a problem without them is under very heavy braking on uneven/broken surfaces when I got a lot of judder as the tyres seeemed to grip then let go, I assumed this was do to the top tube flexing. Fitted 'brake braces' and not got it since. Under normal driving I doubt if one would notice any difference.
A piece of thick wall steel tube £5.00, and a couple of M8 nuts & bolts does the trick. No downside apart from extra weight.
NB watch the route of the brake flex hose relative to the new brace! PJB
