Personally, I don’t trust the sync button. Hence, I never use it.
Beatmatching is about ear and not eye.
I use a DVS system, and I still beatmatch by ear. I’ve seen DJs who have learned the craft by using all kinds of DJ software, rely on the beatgrids of their laptop screens. Yes, It is easier, but what if the DJ playing before you, is using vinyl? There will be no beatgrids and/or the BPM of the track he is playing. In the end, it will still all come down to the basics of this craft.
Don’t get me wrong, there is nothing wrong with learning through software. But there will come a time in certain situations, that you have no choice but to beatmatch manually.
Anyway, just my 2 cents.
Cheers!