I picked up the service parts this morning from my BMW dealer and almost passed out when he told me he could supply the oil for £137

Surprisingly I opted to get it elsewhere.
I was told I needed 05W 30 oil and he recommended either Castrol of Mobil 1.
I was just wondering if anyone knows if the Halfords 05W 30 fully synthetic oil would do as well or am I best sticking to the recommended brands?
Also online I found the Castrol edge oil for about £45 for 5 L but there’s also the Castrol magnitex oil, still fully synthetic and 05W 30 but much cheaper. Could I use this??
Cheers for any help or info because I really don’t know much about oils!
Dave