is not detrimental to performance or engine safety or anything. just means there is no closed loop system going on so the ecu doesnt know how rich/lean the exhaust is of fuel so is using a default map which is generally slightly rich so at worst your fuel consumption may not be all too amazing.

try go through ford to see how much they are and then fitting should be an absolute doddle and dont foget to clear the eml codes when you fit the new sensors.

Actually, get it on diagnostics if you can and see if its both sensors need replacing, might not be.

edit: sensors are made by bosch anyway mate not ford