Its the simplest (if you mean assigning a SELF LEVEL reference to a variable in game-instance). It can break quite easily though so be aware. Forget all the edge cases or gotchas here. If the level is ever renamed maybe or code is moved to a new level and so on. Here’s another solution…
The most reliable way that always works imho… Use the Level-BP to setup an Event-Dispatcher in advance (utilizing game-mode or wherever). Then link an Interface call back to game-mode to invoke the ED. That in turn will then call back into the Level-BP. Been using this for years and it has always worked (even if a level is renamed or code is migrated). Its pretty straightforward to setup ( if you’ve been using the engine for a bit). If not, there’s a legacy official YT tut titled ‘BP Comms’ iirc (Epic chap with red hair),. That will definitely help get you there.
The general consensus on here is don’t ever do anything in the Level-BP. But of course its helpful, especially when prototyping. But always ask yourself this… Can you migrate the code over to a separate BP and just drag that BP into the level, instead of creating code in the Level-BP. 