I was planning on buying the PowerCore II 10000 but I also wanted to use the wall charger for fast charging my phone (iPhone X). Also I wanted to use this charger for powering the powerbank in 4 hours or less.
Does this 2 items do the job?
While the charger you posted will work, this one here is much better and more future proof with power iq 2.0 and power delivery
Do you have a QC device?
You mentioned iPhone X, it is not QC. It does not benefit from more than 5V 2.4A charger such as a Power IQ (not IQ2) charger.
As such for recharging your iPhone X, a Powercore 10000 would recharge your phone as fast as the Powercore II 6700.
The advantage of the Powercore II 10000 is it recharges faster than the Powercore 10000 if you bought a QC compatible charger. IQ2 It will recharge itself with a QC or IQ2 charger is 4 hours.
These are all the chargers which are QC or IQ2 output
This is thus a decision of size of charger vs cost.
The first and last charger I linked to is dual-port, one IQ2, one PD which in effect would do IQ, so you could use it to fully recharge your iPhone X and in parallel recharge your Powercore II 10000 both at the fastest speed. As @elmo41683 said the most future proof would be the 1st charger so its a cost vs size vs future decision.