Roav R5121 Roav Smart Car-Changer Spectrum

No this will not quick charge both devices at once. One port is QC3.0, the other is Ankers IQ tech, which charges at [email protected]. If you find an Anker/Roav charger with IQ3 tech, that meets the standards of QC and will fast charge both devices even if the ‘fast charging’ isnt displayed(its not displayed because its not using a qualcomm chip, but using Ankers patented chips and tech).

Yes, it can charge either of those types of phones individually without having it affect the phone's performance.

Yes, this will work fine for a Galaxy J3.

Yes it will work perfectly, I use the top for higher charging rate although it may not matter which one if your only using one of the two ports