It's pretty jarring.
He still curses as much, but watching the UK Kitchen Nightmares, he's horribly reasonable. He talks frankly to the owners, nearly in a whisper, saying things like "Look, this is your dream, but this shit is fucked up. Your restaurant is in decay, the place is fucking disgusting, and your staff doesn't respect you. You're going to lose this dream if you don't turn this around". No melodramatic music, no camera tricks, no drama, no "WHOOOSH! KITCHEN NIGHTMARES CHING CHING!"
Whereas in the US one, Ramsey will drop into a shitfit over literally nothing. He'll see a piece of gum that the previous customer had stuck to the bottom of the table and go down the hall dragging the entire table behind him, throw it at the owner yelling "LOOK AT THIS FUCKING SHIT! IT'S FUCKING DISGUSTING! I WOULDN'T WIPE MY ASS WITH THE SHIT YOU SERVE IN THIS FUCKING SHITHOLE!" And then he turns it around in 10 minutes and the owner has to walk into the big reveal to the fucking theme of The Chariots of Fire and everybody breaks into tears, cutting immediately to the credits with "Woosh! Next time on kitchen nightmares! 'My restaurant is a wreck, my brother lives in the kitchen, is sleeping in the oven, eats the money directly out of the register, and shits on the tables while customers are still eating and he thinks everything is fine!' 'YOU HAVE GOT TO BE FUCKING KIDDING ME THIS IS UNACCEPTABLE'"
It's insane. He's like an entirely different fucking person depending on what side of the ocean he's on. It's almost admirable, as I'm sure he's 100% aware, and knows exactly how to appeal to each audience.