If you buy the tanks (2-100) and or tank (1-500)you own them. You can then pick and choose who fills them. Meaning you can shop around. If they set the tank, then you are leasing them. Meaning you are only going to buy gas from them.
Pros to leasing the tank. If there is any problems they have to fix the problem. When leasing you can also get in on their budget plan usually. Or even better some companies offer pre buys. Propane companies buy all the propane for the year at once. They always do this when the market is lowest. Usually around June. If they offer pre buys, then you can buy what amount of gallons you want at that said price. So you can purchase your years supply all at once also. Then they just come once a month and top off your tank, deducting what ever they put in from what ever you purchased. Therefore you are not subject to market swings.
Cons of leasing, they expect you to burn so much propane over certain periods. If you aren't going through enough gas for it to be worth their while, they'll come get their tank.
From my experience in the industry. You are better off finding a local mom and pop dealer than to be at the mercy of a large Corp dealer. Hope this helps you get a little closer to being done.