Pre-diluting to that extent is an easy way for the seller to maximise their profit by simply adding water, and without a detailed chemical analysis it would be impossible to say whether it was a true 30:1 mix (actually the normal 1oz to 1 quart would be a 32:1 mix), and may well be diluted a lot more in reality. StuMac don't give duff advice, so the standard mix should be fine for obtaining a good stained finish.

But what works well on light wood won't be as effective on a darker wood, so I'd always look to buy something more concentrated that can be mixed as necessary to suit the situation.