A lot of folks use the propane bottles without incident. And refill them, without incident. And use the converter hoses, again without incident.
However, as tblue notes the use of them may be illegal and this is because those throw-away bottles are uninspected, so they can rust out without your realizing it. Or, the little rubber ball (that's all it is) that seals the neck can misfit or leak. In both cases, you can wind up with an explosion. The fact that most folks get away with it "forever" doesn't mean it is safe. After all, the propane/natural gas industry tells you those are safe fuels--but a number of homes and businesses get in the news in the US every year when they blow up from gas leaks, one way or another.
IF you choose to use them, you MUST either know that the gods love you, or treat them as potential bombs at all times. By all means use them, then shut, disconnect, secure, and stow them on the rail or someplace where they can't leak into the boat. A friend of mine was stowing a dozen of them on a 42' boat some time ago, for lantern fuel and other uses, and the propane sniffer in the bilge would go off at least twice a day--with no trace of a leak "sniffable" to either of us. But something was still leaking.
The other cheap stove that some boaters use (with the same dangers) for occassional cooking is the butane stove sold in most oriental supermarkets and now some flea markets, about $20 for one burner in a box/case, uses a can (8oz? 12?) of butane than snaps and locks in. Cheaper and smaller than the propane rigs, not as hot and a little more expensive but if you only need it once in a while, i.e. to boil one pot for dinner and one pot for the kettle...That also works if you remember that fuel is, after all, designed to explode.