I have an HP Scanjet G4050 flatbed scanner. It can scan 16 slides at a time..but it is still slow because you have to insert the 16 slides in the frame mount provided. The quality of the scans would certainly be acceptable to most people. However, I am picky so I would rate the quality (Clarity) of the output to be just slightly less than optimal. The problem I believe is that the cardboard slide frame prevents the actual film from being in intimate contact with the glass of the flatbed scanner..therefore the clarity is slightly "OFF"
I have Purchased and subsequently Returned 3 different cheaper ($100) 1-3 slide dedicated 35mm scanners.. The clarity of the output was NOT acceptable.
Professional services are NOT cheap...I think about $1 per slide if I remember correctly....and clarity is not guaranteed.
NB