I also know a SWE who bought SLK despite all rational inputs from friends and relatives. Then in 3 years he changed it into VW Passat after he married and his w

I also know a SWE who bought SLK despite all rational inputs from friends and relatives. Then in 3 years he changed it into VW Passat after he married and his wife was expecting a kid. That cost him some money as he needed to sell the car relatively quickly. If your friend cannot be stopped getting a fast car, try to convince him at least to get Tesla which is faster than SLK and can be used as family car.