Sounds like the clutch is dragging a bit to me, my old fiesta turbo did this and the pressure plate was shot. Have they put correct clutch and bearing in, also is self adjuster working ok on pedal. All you do when you put it in a forward gear first is engage with synchro and this stops or slows down the main shaft in box which then enables the non synchro reverse to engage ok, not good long term to be honest. Go back to whoever fitted the clutch.