we have a coleman (i think) 12v fridge on our other boat. it came built into a little kitchen type setup on our pontoon. at first we were going to tear the whole thing out for extra space, but then we came to really like the convenience of a fridge. when we bought our mc, we struggled with the idea of adding one to it. in the end we ended up just using a cheap "marine" cooler that fit behind the drivers seat. our decision was based on the fact that if we are going to be gone for a long time either anchored or visiting friends on the lake, we'll be on the 25ft pontoon which is way bigger than our 02 X30.
to us the biggest downside to a fridge on the mc was size (bigger than the space we wanted to put a cooler) and need for power. the need for power isn't a great demand, but if you are going to run it for extended periods of time you will need to plan ahead. the best solution i found on the pontoon was to add an ACR to the dual battery setup that came from the factory. i rewired the boat to act more like a cabin cruiser with a "house" battery and a "start" battery. the only load on the start battery is the starter. once the start battery gets fully recharged and exceeds 13.6 volts, the ACR combines the batteries and then the motor charges the house battery. when the motor is off, once the house battery drops below 13.6v, the ACR disconnects and isolates the batteries so only the house battery gets discharged. this lets me run the fridge non-stop during the day and not worry about getting home. i also wired in a dual battery charger to let the house recharge overnight. if you go this route, i highly recommend adding a 2nd voltmeter to your helm so you can monitor both batteries independently. this lets me watch the ACR kick in and gives me peace of mind that everything is working properly.
obviously the big up side to a fridge is the convenience. turn it on and load it up. it really helps if the stuff you put in is already cold. for us its easy, as it comes out of the fridge in the house and goes straight into the boat fridge. i've never counted, but i can probably fit close to a case of beer as well as plenty of non-alcoholic drinks. then there's the cool factor. its fun to be visiting friends at their docks, offer them a beer, and tell them "its in the fridge".