I always used a folding key in my bike - 88,000 miles worth. Â I never had a problem with it - either falling apart or being rough on the tumblers.
Very cool, indeed.
As far as the key fob goes, I don't think it would add enough weight to bother the lock, but I didn't like things on my key because they tend to scratch up the roundel on the dash panel.
Before I got real riding pants, I just kept my key in my watch pocket of my jeans when it wasn't in the lock.
BTW - if you are going to ride in jeans, make sure they are the good ones made for hitting the pavement at speed. Â http://www.dragginjeans.com/
Of course, your still don't get ballistic padding like GOOD riding gear.