I have the HP-5370C which is smaller than my old scanjet and that's nice. I have goten some scanns from it, but it doesn't always work--that is, the computer does not recognize that the scanner is there, on and plugged into the computer. When I launch the HP software, I get "SCANNER NOT FOUND." So have to seek help from HP on this.
I have used the adapter for scanning 35mm chromes and they seem to be ok for email and quick prints. I usually take my chromes (transparency film) to a service bureau to be scanned on a drum scaner at considerable cost, tho. They are then output to what's known as a "digital waterproof" which has unbelieveable color fidelity and clarity. Of course it's not cheap and does involve a high-quality scan. But to me, it's worth it.
Anyway, back to your concerns; My scanner came with both Win & Mac software and a USB cable. There is no on-off switch--it is turned on when launching software. It scanns something like 8.7 x 11" size original art. The slide scanning adapter is a square light-box which lies ontop of chromes on glass. I have not scanned negs with it and don't plan to. I got my machine from Comp USA. And that is about all I know--hope this helps you.