Until recently I thought that the only genuine thing about GM oil was the sticker on the can, and that it was a basic 10w 40 that the oil companies sold to other companies like GM and Halfords to brand up as their own...... So I could never really understand why everyone on here was raving about 'Genuine GM' oil, and thought to myself 'What's this genuine thing all about?'
'Are there fake GM oils about?'
etc etc...
So having looked into it abit more, I now understand that GM oil has been formulated specifically for GM engines and it'll be interesting to see if there is a noticable difference when I use the GM oil for the first time....... I'll keep you posted! 
Its a good quality oil at bargain price, and a 'known' item, tried and tested in our cars. The question is, given the TC price, why wouldn't you

Its cheap enough, 3k oil changes are feasible, and this makes it a better option than any ultra expensive oil, such as Mobil1, left in for 10k...
The only oils that I'd actively avoid are Castrol GTX and Castrol Magnatec, which seem to block the breathers on our v6 engines, esp if used for short runs...