I don't like it. You already have Julio and Percy as your starters at WR. If you trade away Ridley that leaves you with no real depth at RB. I don't think the marginal difference of gaining maybe 2-3 points/week at most over Julio & Percy is worth the depth sacrifice.
Standard Non-PPR w/ FLEX
QB: Matt Ryan
2 RB's: Foster, Matthews, Murray, Spiller, R. Bush, J-Stew
2 WR's: Percy, Julio, Nicks, Cobb
TE: Graham, Witten