Garages tend to use a semi synthetic oil in general.
Every Vaushall dealer I've used uses 5W/30 fully synthetic now which is the correct spec. Most new cars built in the last 5 years or so need fully synthetic oil to cope with the extended service intervals. Yes you can mix brands but if it's a VW / Audi / Skoda they seem to need really weird and very specific oil specifications.
Don't forget names like helix one ,mobil 1 and so on are just names used in the UK when you travel to other countries they have the same oil but different names .When they come out of the cracker they only have so many recipes the companies then buy it and put fancy names on the stuff and charge extortiate prices.In the UK vauxhall/opel oil is unbeatable for price and quality everything else is just hype.
![2021 Nissan Qashqai 1.3 DiG-T 160 [157] Acenta Premium 5dr DCT](http://images.honestjohn.co.uk/imagecache/url/crop/90x60/https/assets.heycar.co.uk/t_default-export/f_auto/application_assets/vehicles/pictures/da990225dbcac5ecfadc85d8ad4e2654/690936625217cd1efba5c9cdd4bc42f1.jpg)
