All tags or hashtag systems don't sound very efficient to me.
Both authors and readers need to use tags matching the same spelling and authors need to remeber to do it a priori.
The openess of it means that unfortunately anyone can run bots and completely attack and ruin certain tags. This is solvable with automation and human moderation but unlike with reddit style communities where only a handful of passionate moderators have to clean up, with open tags every user needs to find a way to do it which is terrible UX.