Chemical drain cleaning - acid, base or something else?
Many of the commercial products are buffered in some way to try and reduce the impact on metals, since DWV plumbing may commonly be made from copper, brass, lead, or iron, as well as plastics. In the USA, aluminum is not, to my knowledge, a common drain pipe material.

Sodium hydroxide (lye) is primarily of use against grease based clogs, as it turns the grease to soap. Of course, it only turns the grease it contacts to soap, so if it flows past the clog it will only affect a small amount of a grease clog.

Boiling (or at least very hot) water is another approach, though it is not an approach to use on a toilet (commonly sealed to the base with a wax ring.) Adding sodium bicarbonate (baking soda) or sodium carbonate (washing soda) can add some of the saponifying effect that lye has while being much safer for you than handling lye.

In general, if you have cleaned out the trap and still have a clog in the drain lines beyond the trap, mechanical means (a drain snake) are much more likely to solve the problem than chemical solutions. 

Hair is, by far, the most common component of most clogs. There are some drain cleaners which purport to be specifically formulated to attack it - from what I recall, independent test results were not encouraging, perhaps because hair in a drain clog is coated with a variety of other substances. Physically removing it works.

Acids can indeed affect metal pipes badly - I've recently seen a copper drain line where 25% of the diameter was just gone due to acid corrosion.