I doubt you will see 2.1amp charge. I have not tested the mentioned chargers. I ran a direct wired 12volt outlet to the backseat for my daughter. I pulled the fuse at the battery and placed a multimeter inline measure amperage. I used cheap and expensive chargers and usb data cords withe various Androids phones/tablets. None of the devices was a gs4. There were two gs3's. I saw a momentary spike to . 94amps. Most devices/chargers were below this level. I did not use a dedicated Android charge cable (data +/- shorted).
If you put the ammeter between the charger and the battery (fuse at the battery inline), and measured current then you're looking at the current on a 12 volt circuit (actually upto 13.8v). This is the current the charger is pulling from the car, not what it's pushing to the phone.
Take 12 × .94 and you get 11.28 watts. At 13.8 volts it's 12.97 watts Then divide by 5.1 volts at the plug to the phone and you'll see 2.21 amps at 5.1 volts at the phone (based on 12 volts on the input side), and upto 2.54 amps at 13.8 volts (not counting for loss in heat/resistance). So it's entirely possible that one or more of the chargers you mentioned is capable of putting out 2.1 amps at 5.1 volts.
To see true current to the phone you'd need to put the ammeter in between the charger cord and the phone itself. There are also apps that can run on the phone and which will tell you how much current the phone is pulling during charge, based on the phone's actual internal charging system monitor.
Here are two that I know of but there are others...
https://play.google.com/store/apps/details?id=com.acorilhas.opochargingcurrent
And
https://play.google.com/store/apps/details?id=com.gombosdev.ampere
Below is a reading from opo with my phone on Turbo Charging while at 60%.
It clearly shows at least 2.2 amps going to the battery.
And here's the same app reading while charging from my 10K portable battery on the 1.1 amp port.
What's strange is that the following is a reading from the same portable charger but in the 2.2 amp port, and its actually lower... I'm also not getting an average on the 2.2 side and the levels are bouncing all over the range from zero to the max.
I'm beginning to believe the 2.2 amp side of the charger is either defective or the phone is simply working hard to curtail the current rate to protect the battery.