1 1-16, 1/2 inch drive with long breaker bar using extra leverage. Best to use impact wrench if possible. Easy peasey. The above are just my personal opinons as a diy homeowner.I have some heaters with little clearance overhead. It would be hard to remove the anode rod. My questions are:
1) How long is a typical anode rod?
depends on water heater. about 2-3 foot avg. I've seem them longer.
2) How would you get the old one out if there is little clearance (2' or less)
over the water heater?
you could cut it and use flexible or telescopic one to replace it.
3) What type of metal in an anode is preferable? most are magnesium or aluminum. Preferred is magnesium, imo. Really depends on type of water you have.
4) Are those linked flexible anode rods good? (I fear they will fall apart at the links) I don't have any personal experience with them. If space is limited you may not have a choice unless you want to drain, and disconnect/tilt water heater to change it out. You can google customer satisfaction and read up on it.
4) Is there a standard sized socket for removing anode rods?