The big question is always" Does Medicare pay for tube feeding formulas?" Yes, the formulas and supplies are covered by Medicare Part B and most insurance.
Formula won't be covered unless it is the primary source of nutrition and you can't eat well enough to maintain your weight without it. Medicare covers tube feeding formulas if they provide all or the majority of your nutrition. Being able to swallow small amounts of specific foods doesn't disqualify you, but if you still eat most of your meals and just use the tube feeding as a supplement or convenience, Medicare won't cover it.
A form/documentation by your doctor is required for Medicare reimbursement and a diagnosis of ALS covers all the requirements.
Standard tube feeding formulas are covered as well as special formulas needed by diabetics, kidney or liver patients, etc. (Do an internet search for Medicare Part B Enteral Nutrition Reimbursement Manual.pdf. It lists many but probably not all covered formulas.)
Natural formulas may be covered if your doctor documents an allergy or intolerance of standard formulas. A preference for a natural formula isn't covered.
The cost of foods and supplements used to make your own blenderized formula is not covered.
If you get formula through a Medicare provider, compare the amount of your copay against the price you would pay buying it yourself online - no prescription needed. Often prices are so jacked up by Medicare approved providers that you end up paying more copay even after Medicare limits the amount Medicare will pay.