£79 is a very good price for the forge 007p diverter.
The split R is a more complex and pricey valve. Opinion on these is 'split' (excuse the pun) sounds like they are tricky to set up correctly, some love them some dont like them.
Basically the 007p is a straight replacement for the stock item, does its job well and is reliable. These items divert the air internally so the air is not 'lost' and is quieter.
The split R does not divert all of the air internally, it dumps or diverts some of the air externally and this is for people that want some noise.
(ECU expects air to be recirculated, so a valve that dumps all the air expternally is not recommended)
IMO get the 007p.
Most people get one before issues arrise. You can leave the stock item, however like most thing, when they fail there is potential for further costly damage as a result. (you dont really want anything breaking in the air inlet system..)