I did this when Rings of Power came out. Full transparency, I’m pretty mid on LotR in general. With that said, this is a very cool experience if you’re a fan of the work or have never seen these in theaters. Some criticisms I have: you can really tell that the scenes in the extended cut were not intended for a large format, high fidelity screen. You can tell which specific cuts in battles are extended and which ones are theatrical. Additionally they use greenscreen for Hobbits more in the extended cut and it looks bad. Also, if you haven’t seen LotR and aren’t a huge fantasy nerd, I’d have a hard time recommending this. 12 hours of movies is a whole lot of time and the the theatrical editions are great! Return of the King won more Oscars than any other movie in its theatrical cut!

Overall, very fun if this is for you and even if it isn’t these movies are great. Whatever you think your opinion about this is going to be, you’re almost certainly correct