yabu, slings are great and i still use a sling with my 18mth old dd and she is big for her age, wearing age 2 clothes, they are fine and if anything better if you have a child on a scooter as you can keep up wiht them more easily and grab them if they try and scoot off wihtout having to stop, park the buggy, put the break on etc, infact the other day i had the buggy with ds4 in it bizarrely as he was tired and dd was walking and toddled off towards the road, scared the life out of me as we were going up a hill and i had to quickly stop and put break on buggy and then run after dd, if ds4 had been in a back carry it would have been much easier to grab dd, or vice versa.
re babybjorn i would say yes they are crap as they arent good for the baby, they may seem happy but they arent very good for a babies hips or spine, which is why i wouldnt use one, its very easy to research.
i have had at various times, two wraps one woven, one stretchy, a moby wrap, a mai tai, a wilkinet and some ring slings, have passed some onto my sister now who has a 6mth old and loves using them, but i still use ring slings for dd, always keep one under the pushchair, they are a godsend :)