This topic always comes and goes for every HDPE or PET container we use for brewing. But your link basically says not to use non-food grade material!
The difference, AFAIK, is between food grade and non-food grade. Food grade(FDA) has (supposedly) followed all the rules about how and from what machines, dyes, chemicals(like release agents) it was manufactured from/with; non-food grade is not. The non-food grade "might" be just as good or then again not. Like what the extruder had on it before, was it cleaned, were recycled materials used(that contained chemicals), etc. You just don't know with non-food grade, for certain.
There is a different, more expensive restrictor:
http://www.chicompany.net/insta-balance-foam-preventer-859.html
Haven't used, but they look like stainless.
Like a friend used to say, you pays your money and you takes your chances....