Ridley had 1,200 yards and 12 TDs in 2012. It's not hard to imagine a return to the playing time and form that saw him finish as RB10 in standard, and RB15 in PPR.
Ridley's problem isn't that he fumbles... or rather his problem isn't *just* that he fumbles. He has had some poor timing with fumbles at times. He also has the distinction of playing for possibly the least tolerant coach in the league, in regards to turnovers. When he's on the field, Ridley is a very talented RB. However, he showed last year that he's able to fumble away opportunities, and it's reasonable to think that the same could happen again this year.
Ridley finished as a low-end RB3 last year, putting up a 178-773-7 line in a down year. However, he likely did not return RB3 numbers for a lot of his owners last year - as they were often left frustrated and wondering whether or not to start him.
Some preseason struggles with fumbling have served both to give us pause for ongoing concern, as well helped keep his ADP at a reasonable level (late 6th round). While that's a two edged sword, so to speak, Ridley is a decent value at his ADP. While you may be inviting some weekly frustration onto your team, I see a guy in Ridley who is being drafted not too far from his floor and offers plenty of upside. Your worst case is having a guy you can plug into your flex as a bye week/injury filler. Your best case, however, is having an automatic weekly start. Worth noting, we do rank Ridley higher in standard (RB29) than we do in PPR (RB36.)