I'm not sure it really would
It really would. I wouldn't buy a flat that wasn't at least share of.
For £3k it's a total no brainer. I disagree that there's no benefit to owning a share, with a share you have equal power, if the owns it he has absolute power.
Get back round the table and explain that the access thing is not about him because he's so nice and reasonable* but in case he sells and you get a nightmare neighbour.
*doesn't need to be true