If heaters are the same in both irons than lower supply voltage will result in slightly less peak power.
If the heater is designed for 70W at 24V that means it pulls ~3A from 24V and has 8Ω resistance.
You can do the math how much power you will get from 19V and how much current the supply will need to provide, but it's gonna be less.
That being said, I'm not sure if I would trust any PSU from AliE. Bottom of the barrel PSUs can be quite bad, with poor reliability and electric and fire safety hazards.
There is some chance that maybe the 19V version uses a different heater with less resistance, like there is many variants of the 936 style irons. You never know with those knockoffs. Do your research
edit
If I were to buy something like that, I would look for an option of 24V rated unit sold without PSU and buy some brand name 24V/3A PSU locally.