Mine didn't really feel much (if any) different while riding, but if you have a center-mounted dual-legged kickstand, it'll leave your front wheel up in the air (a little bit) and one of these can stop your wheel from flopping to one side quickly (and making the bike fall over). It's also helpful when you're loading a front rack and don't want the things to flip everywhere. Not a real need, but it does have certain defined uses that make it nice.
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Bikes: 1996 Eddy Merckx Titanium EX, 1989/90 Colnago Super(issimo?) Piu(?), 1990 Concorde Aquila(hit by car while riding), others in build queue "when I get the time"