If you shoot a lot of different processing types, I understand. Do you have your own scanner? I use their scans for sharing online and/or previewing (same with included prints) and if I want one or two photos to print, I'll scan it myself at any size I want/it can handle. It's much cheaper in the long run to do it myself, as much of a pain it is. Their same day processing with free overnight delivery back is awesome. Like I said, it seems their business model is more IPS than just process/scan.
When I send them my samples, I send some quick "7MP" scans and the 8x10s they sent back were great.
I don't have my own scanner and at this time do not have much interest in getting one due to time constraints. I want a one stop shop where I get the film developed and hi rez scans all at once.
Out of curiosity I tried to scan using a DSLR (D750), light pad, macro lens and a flextight film holder. For colour I could not get close to match what real scans did, and in B&W it was ok until I compared the sharpness to real pro scans. Then it was lacking (but would have been fine for internet postings).
The sample prints were good - I had uploaded 4 files as per their instructions - but what was interesting was that they gave prints showing what I had uploaded w/ no corrections by them, and the same image with their recommended corrections. My monitor is correctly calibrated using an Xrite device, which continuously calibrates it. All their corrected images were a little more contrasty losing fine details in the highlights. Their uncorrected prints were great, just how I wanted them (which is why I always refuse the option to have a lab 'correct' my images), so I can see using Miller for printing services.