Question on Truck Campers

Many truck campers have a small window in the front wall that aligns with the truck rear window. Sometimes it can be used for rear visibility but most are too small for most adults to pass through. The ones that do have a large enough window require a flexible boot joining the truck cab with the camper and some people use this feature for their pets (as far as I know). I would be curious to find out if there are any people here who actually go back and forth ? Your travel trailer didn't allow it but I can understand the major feature of almost all Class As, Bs, & Cs that do allow it. Like everything in life, there are always pros and cons. The nicer Class Bs are quite expensive if comparably equipped as a good truck camper.