I had a Ross 10sp (Eurosport?) with FFS (front freewheel system). A couple things come to mind:
On the freewheel side in back, there might be a noticeable / annoying amount of slack to take up after gliding to engage both freewheels.
On the fixed side, you have the risk of catching something on the chain, possibly complicated by the fact that your feet might not (initially) be moving in sync with the chainring.