Included charging is a core part of the ‘one monthly fee’ proposition and certainly is a USP for Onto, the other major one being the no deposit, 30 day minimum term.
Included charging won’t mean everyone charges from the included networks all of the time (but we know some do), just as not everyone uses the included 1,000 miles a month (but some do, and some need more, hence mileage packs exist).
Coverage will differ in different areas, the onus is definitely on the subscriber to check coverage and make a decision when signing up. While your home area might not be covered, any longer trips will undoubtedly have you passing by included rapid chargers (deepest Wales and Scotland North/West of the central belt aside maybe) and these are the ones that would cost you the most if you didn’t have these cards included (Especially Ionity!). Similarly, folk who don’t have driveways or anywhere to park with an opportunity for home charging will have to find something that works for them (we’re in this bucket and so far it’s a mix of the Shell network rapid up the road and free AC chargers at supermarkets when shopping)
Onto almost certainly gets a much better rate at scale and on a partnership basis than a consumer would with the charging networks as others have said. Levelled across the entire fleet it’s likely nowhere near £50/mo for every vehicle. At a £50/mo discount I could see appeal, but also I love that charging is included and every friend I’ve told about the service that’s one of the things that really has them saying “wow that’s a good deal” - it gets equates to fuel cost which is a huge portion of operating cost for a car.
(My two cents only!)