I just looked it up on the site above, and it does not break down whether his fumble is from a return or an offensive play.
So he has 3 total fumbles, all from his rookie year by that count. Maybe my bias against him is from that rookie impression, with the addition of his inability to break out on offense last year - he got fewer touches on offense last year than he got his rookie year, and I think that justifies some pessimism.
I would say that I am not very fond of players on offense that are only effective on gadget plays. It seems to me that the element of surprise is less effective when the gadget player can't contribute on more routine plays.