One of the best things about the show is the fact that they researched everything down to a tee.
The ways that they use to make methamphetamine in the show - such as pseudoephedrine reduction in the first season and combining phenylacetone with methlyamine in the presence of aluminum in a tube furnace in the rest of the seasons - are actually real ways of synthesizing methamphetamine.
Only thing that bothers me is the fact that they keep having to find methlyamine which is ridiculous. Methlyamine can easily be synthesized in your bathroom sink! An easy way to achieve this swap is to “bubble” ammonia (a gas) through methanol (wood alcohol) that’s been laced with a dehydrating agent like Silica gel. All of these chemicals you can get at your local hardware store.
Other than that - since methlyamine is so elusive in Breaking Bad - they could also use Phenylalanine (a vitamin supplement that is a phenethylamine derivative). All they would have to do is crush up the vitamin supplements, add lithium aluminum hydride (which is found in lithium batteries) and pour in some anhydrous acid and the phenylalanine will combine with the lithium to form methamphetamine.
I don't know how hard getting anhydrous acid is, but that seems simpler to me than combinign P2P (phenylacetone) with aluminum.
I'm no chemist, but that's just my two cents.