Hey their William_F,
Yep, that 50/50 mix of the Isobutyle (Rubbing Alcohol) and distilled water is the same basic components used in the production of Quick Detailer, only without that nice fragrant scent that most manufacturers introduce to the mix to psychologically make you feel a nice pleasant cleaning sensation when using their Products. Overall their i no difference except the cost.
So my best advice is, if you are not into all the overpriced nice smelling stuff, then I would go for the 50/50 mix for sure! As you plointed out, it is way cheaper, and does the same effective job.
That is my 2 cents for what its worth anyways. Just a lot more bang for the buck!
Thank you for your question, and i will catch ya later on.
Candyman