Actually, free housing and a food allowance (how much?) sounds not too bad. Perhaps if one enjoys the teaching it sounds pretty good. I suppose no disposable income to travel or indulge in other things you may like would be the downside. As well as no ability to save/invest for the future?
Food allowance can be free food at hotels (if your center is at a hotel) which is the moist common. The life is not bad, but it does require some sacrifices. When I left the States to do this, I knew I would likely never retire, have a nice car, high-end gear (laptops, cameras, etc) own a home again and much more but I was ok with that. It is a lifestyle I have chosen to live.
Would I like to be able to afford more dive gear like a Sidemount CCR, a drysuit and a nice camera and rig? Yes I would but the gear I have now is very good! Would I like to be able to travel to take a cave course in Florida or Mexico, maybe a wreck course in the Philippines? Traveling to be taught by the best is something I would love but it is not in the cards at this time. I also want to own my own center/resort but I love the instructor lifestyle. Long days but they are filled with seeing the smiles on people's faces and making friends for life.
Some do this for a few years and get back to the 'real world' but for me, this is my life and I have no desire to give it up.