I have a USB current meter that is something like one of these
https://www.amazon.com/USB-Charger-Doctor-line-Voltage/
You place it between the charger and the device you are charging and it shows you the current used. An Apple iPhone charger can supply up to 1000 ma. Let's say the battery in the device holds 3000 milliamp-hours of power So then a 1000 milliamp hour chargr will need three hours.
My bike lights and phone all will accept the full 1000 milliamps the charger can supply. The charger in you link claims to suply only 500 milliamps so it would take twice as long as my Apple charger.
The next question is how many hours a day will you ride? It takes 3 hours to charge my larger bike light using an Apple charger if the light is flat-dead. So it would take 6 hours on the 500 ma charger.
What you need to do is measure how much power you devices used. Buy the amp meter and keep notes on the charge time and multipley milliamps and hours and then you know how many miliamphours per day of charging you will need. The charger you linked to supply 500 milliamp hours per hour.
You can dramatically reduce you power needs by placing the pones on "airplane mode" and then only using them for minutes at a time when needed. Switch it one for 10 minutes to let it download any texts then back on "airplane mode". In this way a phone battery can mabe 4 days. Same with lights. Keep them in low power daylight flash mode.
I would brig spare lights that use non-rechargable batteries as a backup.
Bottom line is that a 500 ma charger is weak but you will have two of them and you can cut your power use. I'd run experiments at home for a few weeks and the USB meter can be informative.