SWL causes most of Feng's evasive moves (and indeed most of his other moves) to whiff. UF2 in particular is very linear. While DB3 tracks and crushes highs, it is launch punishable on block, and B4 has low reward. Step-guard is a great option to beat his stronger homing moves. iWS1 will track, but not many Fengs do this.
Feng's punishment is not that good, with no i12 and his i15 launch punisher having range issues. You may be able to get away with murder, depending on the matchup & the Feng's level of knowledge.
Remember to backdash. Feng SS4 is more like a Demoman than a hellsweep, and a clean hit is rarely guaranteed. Many of Feng's pokes, like his DF1, lack range or have lots of pushback on hit.
After D2 hits, Feng is -1 and in crouch, with a fullcrouch arsenal that can mostly be SWL. This includes his WS4. Don't allow him to bully you with this situation.