Same effect on the hips, ideally the knees should be above the hips. in the bjorn they just hang straight down.
I dunno, I went shopping the other day and saw about a dozen daddies wearing babies forward facing in bjjorn style carriers, all the babies just looked so 'rabbit in headlights' at everything.
If you do want to do it, I would suggest somewhere thats not to over stimulating for LO, a walk in the park rather then a busy high st/shopping centre. and only for 15/20mins max.