UK Official services do state that they are not the GRO (Section 9) but offer a service of 'Official' UK Documents. It should be obvious that they are not a government organization. from their URL (NOT .gov or .org but .co.uk!) .
When I ordered notarised/apostilled documents from them (2 years ago) they delivered ON TIME and ALL my documents were fine and as agreed.
This is a useful service to those who do not have a UK postage address or those who want to reduce postage costs by having all their documents delivered to them wherever they reside in the world. Useful for digital nomads, travellers etc who need these documents.
Anyone complaining that they 'deliberately mislead' must be very uneducated or computer illiterate, in which case they'd be better off WITH UKOS since they handle all the admin / postage for them, which can be a headache and expensive.
The additional cost I think is moderately overpriced but the amount of headache and hassle it saves you is a godsend if you are not in the UK or do not have a UK Address.
The name UKOfficialServices is a good one, I think, because foreign officials like the words 'Official' and 'Services'. Don't ask me why, they just do. After all it they do provide Official Documents as a 'Service' and are based in the UK. This is legitimate practice and all my documents are legitimate and I got what I pad for AS AGREED and they delivered, even though it is moderately overpriced, it SAVES HASSLE!