If you're going to be plugged in all day - it's incredibly slow charging in real life via the usb port. Virtually any 12V_outlet-to-USB adapter is going to charge your phone at least twice as fast.
At the expense of battery longevity. Charging twice as fast is convenient but also means extra heat which hurts the battery. Remember, there's no temperature management system active which turns on some fans in a smartphonelike there is in a volt. The best the phone can do is sense it's getting too hot and throttle down the charging to compensate.
This won't matter if you upgrade phones every year, but it does matter to those who hold onto their smartphones for 5+ years before upgrading. My wife still carries an iPhone 5 (4.5 generations ago....5, 5s, 6, 6s, SE-sort of based on the 6s CPU, 7). Sure you can replace the battery, but my daughter's iPhone hold button was never the same after a mall kiosk repair guy replaced her battery. She spent 2 years using the accessibility home button on the touch screen to workaround this. Luckily she was able to turn this feature on before the home button broke completely.