Well, it would certainly put you in charge.
I've tried both Peak Imaging (excellent for E6, I found some years ago) and my local Tescos for scanning at the same time as a C41 D&P package. At Peak I requested their very best Archival Gold service, and paid handsomely for it. At my local Tesco's in Wolverton, I paid an extra 97p and had my results when I'd done my food shopping. Other Tesco stores may charge a little more if they have to send the film away.
The Tesco CD is limited resolution, but otherwise is fine. The less said about that from Peak the better.