We have a booked 143/150 combo booked out every morning before they split at 08;45ish.150/1s working in multiples with 150/2s, 153s, 158s or other 150/1s are common around Bristol. Weekends sometimes throw up some interesting combinations, as do summer services to Weymouth. I have seen a 143/150 combination in Devon before too. Makes it all the more fun when local doors are used for short platforms!
I have seen a 10 coach formation (2x158/9sand 2x150/2) when one train didn't have a driver to take it between Bristol and Westbury so they coupled the next service to the front and run the lot down before splitting it again.You don't see many 6 carriage DMU services around Bath, as HSTs are used for to/from London, and 5 carriages tend to be the maximum for trains travelling in the Avon Valley. That said I have seen a 6 carriage (with every carriage carrying passengers) service before formed of 2 x 3-car 158s. Not sure what the door release arrangement for platforms were. Can unit deselect be used when passengers are in both units?