Perhaps it just bring them closer into the fold and nato accession would be more likely or quicker . And like you say freedom of movement and access to more non military help.Hmmm not sure what the immediate benefit might be. There is always the general benefit of being in a block, closer ties, borderless travel (helps refugees?), free trade… no obvious security benefits yet. As you say NATO is a separate entity…
Pure speculation, but Putin is demanding at the peace talks that Ukraine is neutral. Maybe Zelensky is getting ahead of that - it’s easier for Putin to put a stop to something before it ever happens than if the wheels are already in motion.