I have flown on the MAX from New York Newburgh to Edinburgh back in January 2019, I've flown on the A321 XLR from Lisbon to Toronto and have flown a trans-continental on Air Canada on the C Series. One thing is clear in all of these experiences, it ain't fun compared to a nice wide body, especially in business class. For instance for my trip from Lisbon to Toronto on TAP, I was in business class and they had lie flat seats. Yes the seats do go flat but the J cabin is arranged in a 2 x 2 configuration, meaning the seat width is not sufficient to get either good quality sleep or even in the upright position for 8 hours on end. The MAX was even worse, especially since I was flying Norwegian where all leg room is cut out. C Series was manageable but I wouldn't want to venture out more than 4 maybe 5 hours tops on it