“Get a FN-FAL instead. It is a superior firearm.”
It very well may be, but the M1A takes M-14 magazines which (when last I checked) were relatively cheap and plentiful here in the US. The FN takes proprietary magazines which can be either metric or imperial (depending upon rifle variant) and are not interchangeable.
The problem with M14/M1A mags is the prevalence of after-market "junk" mags, and the relative scarcity & higher cost of reliable GI mags. Unlike the M14, the FAL was adopted by dozens of countries (one reason the FAL was called "the Free World's Right Arm" ;^), and military surplus mags have been coming into the US for decades. Most of the FAL mags you come across are therefore "real deal" military mags, and the inch & metric mags are easy to tell apart...
Metric magazines are also plentiful and cheap for a FN-FAL.