My problem w/ a subreddit is that reddit would show you a lot of stuff that is off-mission for the group and surrounding community. Also I'd expect such a page to be focused around getting people to show up to events rather than having discussions (e.g. the moderation problem is much easier if discussions are only for the purposes of the group; off-topic rants about divisive subjects are easy to squash; you don't have the problem of the rumor mongering about crime which I think is toxic on nextdoor but doesn't cross the line)

I wouldn't mind ads but I'd want to see ads of the old-school sponsorship variety (the running club could see ads for the local running shoe store, one of the local grocery stores, an overfunded non-profit like the United Way, etc.) as opposed to the auction-based, personalized ads that you'd see on reddit. Similarly if a sidebar on the running club had a link to a local board game or ham radio club I'd think that's OK but the mission on my mind is to get people to join the ham radio club where they're going to do comms for the running club, not to maximize time on site.

I have found that Nextdoor isn't toxic, your neighbors are