https://www.flyertalk.com/help/rules#externallinks
FlyerTalk is here for the purpose of sharing meaningful information. Don't simply post a link by itself to another source, such as an article or blog. (See also, Rule 9 — Posting Copyrighted Material.) Posts containing such links should contain enough information so as to be contributive to FlyerTalk itself.
I submit that an external review of a property (that contrasts with other external reviews mentioned in the thread) linked in a FT thread discussing the property is indeed "sharing meaningful information" and well within FT discussion guidelines (being topical and so on). I am not aware that FT has a rule or policy prohibiting links to external reviews that are not contributed by FT users. I would find it fairly objectionable if we were not allowed to link to external review sites merely because the reviews do not conform to a style guide and were not written by an FT user. I find the differences in opinion and evaluation (as well as thorough pictures or video) to be quite helpful.