As a quite frequent AY flyer, my opinion about AY FF scheme is:

1. It is really good only if you fly a lot with AY, you value upgrades on AY metal and if you can reach Emerald with them, then IMO it pays off

2. If you dont fly that much but you can still reach Ruby with them and you mainly fly on AY routes with AY issued ticket as then you will get lounge access quite easily even if flying in coach. For not so frequent AY (OW) flyers this is hard to get with other OW FF schemes

For all other AY flyers I would recommend AAdvantage from Finnish (European) perspective)

Cheers,