Nota bene: those end up as notes on the map which another mapper has to input manually. There's a lot of spam and dubious entries so I often no longer bother entering them, especially in places I don't know or where I cannot verify the information.
I was using Street Complete for some time and was always wondering if using these apps is considered helpful or if it only creates churn/noise. Is there a general consensus on that in the community?
Would it be more accepted to just do a few small, potentially not metadata-complete edits myself or is the review structure (if there is any) geared more towards fewer, more steady contributors?
Did one direct edit once and iirc it took ages to land in the map and I wasn't able to grasp if came from new editors' edits being scrutinized more carefully by too few reviewers, from the nature of the edits (deleting a bunch of buildings after demolition and probably not replacing it with the right area type) or if the release cycle for new edits to be included is just way longer than I would have expected.
As a frequent contributor myself I love StreetComplete and I wouldn't worry about it perhaps generating a few changesets more than strictly necessary (it tends to make one changeset per quest (with multiple amendments for individual answers) and also only during a certain time frame. Sure, that means that adding information to a staircase creates multiple changesets (incline, step_count, surface, handrail), but that doesn't really matter.
What StreetComplete is very good at, in my opinion, is simply QA on the ground. SC asks about features existing on the map (benches, bus stops, shops, roads, barriers, etc.) and some of them might go stale. So asking about opening hours of a shop might cause someone to look and notice that the shop is closed now, or replaced by another one, so in many cases the quests that add detail to objects have the nice side-effect that those are being looked at and reviewed whether they still exist, which otherwise does not happen often. The barrier to adding new data is often lower than fixing or removing outdated information.
And it's such a low barrier to entry, especially for people not familiar with OSM's tagging, since the UX is very well designed for beginners in my eyes (while still being useful for advanced mappers), that you can easily recommend it to people who like those kind of hobbies (e.g. geocaching, Pokémon Go). For me it was an excuse to go outside more, also to places I haven't been, during COVID-19, just to tick off another quest.
The review does not block the data being added, it's more of a request for feedback.
Different maps have different update cycles. The slippy map on osm.org is meant to update as quickly as possible, usually a few minutes, but sometimes there are hiccups. Zoom levels that show larger areas also update a little slower.
As long as what you are adding is up to date/accurate, I wouldn't worry about whether you've captured everything about the features. "This thing is here" is a lot better for the map than no information.