Only Mobil 1 from Halfrauds is good enough for my baby! Also, I've heard that if you buy it on Trade Card they give you a different formulation which reduces your output by 1.25 BHP.
Whenever I pass a drain I drop a quid in it as well, just for good measure 
Seriously, though, that is a real bargain. I must get my ABS application off! I've been buying Chevron (fully synthetic, admittedly) in 20L containers from the local Costco and even that's double the price! It's also made my garage floor a bit slippery. Well, you try pouring oil from a 20L container into something more manageable!
Kevin
If youre in Costco why not just buy the Mobil 1? Its £21 inc VAT for 5 ltrs, as opposed to £45 in Hellfrauds, or £35 with Trade club

And before any one starts i dont care its what i use, and my breathers ar clean as a whistle, which i'm convinced is due to the oil not degrading and blocking up, and i go atleast 10k between oil changes
