Fast pick up, easy drop off, good price and upgrade (whcih I later regreted having bigget SUV in narrow Cornish roads so mind your upgrades!)
Car was clean and ready.
Bristol Airport has short operating hours which is only drawback. I saw pickup box however so maybe there is an option for off hours pickup.
Either way, car rental is always a stress for me during vacation and this one was smooth and easy! Good job Sixt!