Yes, many people have used Flagship check-in and Flagship Dining, which is all that Flagship Business Plus gets you (and a 3rd checked bag).

Whether this is "worth it" is going to be entirely subjective, I would recommend reading the threads here and other reviews online to see if you think it's worth the $500 or whatever. For me personally no way.

Flagship Business Plus???

https://www.flyertalk.com/forum/amer...a-ord-rev.html

Guide to AA Flagship First Dining Qualifications, Access & Related