Construction: 6.5/10 - adequate. Not bomb-proof (like one would like for use on a stage floor).
Readability: 10/10 in the dark, 2/10 in the sun.
Note tracking: 9.5/10 - quick and pretty much flawless.

I used to have one of those handheld tuners by Sabine and boy, was it ever lame. The main problem was note tracking. It took forever to decide what the hell note it was listening to. Tuning with it was tedious and frustrating.

One day the Sabine went missing (no tears were shed), and on the advice of other players, I replaced it with the Korg. Problem solved. It tracks notes easily & quickly and is very accurate.

I've used mine for 4 years with no problems. The construction isn't super rugged, but it has survived at least it's fair share of accidental drops onto non-carpeted floors.

It's a hassle to read outdoors on a sunny day, but it can be done (you have to shield it with your hands after sounding the note).

It can be automatically calibrated to another pitch source, or manually set from 438-444 though I haven't done it in so long, I've forgotten how to do it. (As I recall, it was fairly intuitive for the gadget savvy -- kind of like setting the clock on a VCR)

In my experience, the Korg tuners really work. Be very wary of cheaper tuners that don't work, unless you enjoy being annoyed & wasting money.