Due to the UK being shut off from the European mainland because of the new Covid-19 mutation it is very likely your order will be delayed until further notice. There is nothing we can do about this at this point in time
A good derailleur is half the work. Both a well-running front derailleur and a rear derailleur are of great importance to the racing cyclist. A rear derailleur must run smoothly, accurately and quietly. The most important brands in this area are SRAM, Campagnolo and Shimano.