i was wondering if both batteries are just as easy to replace in both units.
And the 1/8 inch input jack is just as sturdy on both units?
Which unit is more rugged for the long haul, and is there a hold switch on the 120?
For the H1xx, you need a torx driver, whereas the H3xx requires a plain phillips, AFAIK. But once inside, the battery swap is roughly the same.
I haven't heard any major complaints about the input jack on either model, I don't think that they differ much. Both models are well-built and rugged, hardly any difference there.
Since you'll be picking it up second hand, I'd be more concerned about how the previous owner handled his gear. If he was careless, he could have caused stress on the jacks, regardless of it being a H1xx or H3xx.
And yes, there is a hold switch on the 120.
T+ and welcome to Team Iriver! ;-)
/J