- Do you think that it would be a good choice for a beginner?
Yes, maybe.
It has all the basic things for a two channel scope.
- What do you think about Goldstar construction quality?
I cannot comment, I have no experience of Goldstar.
- The Ad says it's non calibrated. Is the calibration process something that the user can do, or require specialized personnel and equipment?
"Not calibrated" could have two rather different meanings:
1 It is working correctly and is within the manufacturers specification, but it has not been "proved" correct in a certified calibration laboratory.
2 It is working, but the calibration is way off. Either because something is worn out or failed, or the local idiot has had a play with it.
If it is 1 then no problem. None of my equipment* is formally calibrated.
If it is 2 then it is a problem unless it is very cheap.
As for calibrating it yourself, for most hobby purposes the voltage ranges can be checked using a stable power supply and a known good DVM.
To check the timebase, you need an accurate time or frequency source.
JimB
* Except my frequency counter.
I have an accurate frequency source which locks to a standard frequency radio transmission.
But this would still not be acceptable as a traceable standard in an industrial environment.