I've used Nippon. They were great. For a little over £2,700 (inc VAT) they picked up my car from Swindon, took it to their workshop, installed a used (not reconditioned) engine that had done ~48,000 miles (77,000Km), tested everything and came to pick me up from the train station when I came to pickup the car in Derby. This was September 2023.
I asked lots on annoying questions and they were very patient, polite and pleasant. The whole thing took just under 3 weeks.
I've used them again since for spares which they post to me.