I just bought the SH56 a few months ago. It has a leaf vac attachment, too. Works just fine and starts on the first couple of pulls. I've shredded multiple bags of leaves with it and it works well, it's only stalled once or twice when a decent sized (too big) stick got jammed in the shredder blades. Blows leaves around just fine and will blow them off the grass just fine, too. (Though I've been using my lawn mower with bagger to pick up lots of my lawn leaves).
My only real gripe is the system Stihl used to change from leaf blower to vac. You have to press down on some tabs with a screw driver to free things up, and esp. the first few times you do it, is a real bear to mess with. You'll know what I mean when you look at it. I would tell your dad to have the dealer SHOW him how to switch from blower to vac with the Stihl and whatever other brand (Echo??) of blower vac they might have to see which is easier.
If he's only going to use it as a blower most of the time, it's pretty much a non-issue. If he was on a residential lot, I'd say go with the handheld. If he'll be using it for more than 15-20 mins at a time, you might think about the backpack.
