Diagnostics

Just purchased my second RR it’s a 4.4 v8 L405, could anybody recommend what is the best diagnostic tool for this vehicle

What year? up to 2017, it's conventional CAN, 17MY on also has FlexRay and different address spaces for those modules still on CAN so that will have a large bearing on what systems (and the cost of them) are suitable.

Sorry should have said it’s a 2014

Autel have good (but not full) coverage as do any 'Launch' based systems (Topdon etc. - but beware poor and cheap clones), it depends upon what you want to do really - there is the SDD option https://www.landyzone.co.uk/land-ro...ted-feel-free-to-add-experiences-help.365631/ but unless you're a bit geeky, it may be an uphill struggle just to get the diagnostics working (and reinstalled every 3 months) as it needs 'manipulating' and unless you've experience of dealer systems (any dealer) it's quite a steep learning curve.
There is also an 'assisted' option - https://osca.online/?#features
If you just want to monitor the powertrain, check DPF values (very useful to know when a regen is occurring so you don't cancel it and end up with oil dilution) etc. then I can recommend 'Car Scanner Pro' www.carscanner.info and vGate iCar Pro Amazon product