As an ultrawide gamer over the last couple years, I'll have to say that unless you're very willing to overlook the notion of having to tweak many of your games to have good support for it, that the novelty of 21:9 could wear off quickly. If you are willing to overlook that, then the immersion that you feel when playing a game that has at least good support for UW is second to none. IMO even more so than VR.
Personally I play a lot of games that have piss poor support for 21:9 like Monster Hunter World, Fallout 4, and Skyrim SE so I am strongly considering switching back to 2560x1440 at 144hz. MHW's ultrawide support is non-existent and the tweaks to force it cause massive performance degradations and screw with the menus, and Fallout 4 and Skyrim SE suffer from ghastly UI stretching that can only be fixed by UI replacement mods that are not perfect. The UI replacement mods also prevent the Creation Club elements from being shown in Skyrim SE, which is an issue for me since I use the Survival Mode CC (got it for free).
If you tend to play games that have poor support, then I would skip it.