720p anywhere should make you run.
If someone paired 1440p with a 720p rear camera ( i have never seen that combo ) well i would instantly think.
1: Those 1440p got to be a lie.
2: This system are made up of old hardware than cam barely pull the 1440p on its own.
It would probably also be so bottom of barrel stuff that you will not see any updates or service on the system.
There is a myriad of make / sell and run away dashcam brands, where you will be out of luck if you have any problems, if this forum covered all these more or less obscure brands the " other brands" sub forum would be 3 X larger at least.
If you are that " pressured" on price, i think you will be better off just looking for a good front camera, dont get me wrong 1080p i would still say is OK as a rear camera, but i would not buy that if i was looking for a new system.
In my perspective only 1440p and 4K count these days, so that is what i would personally look at. ( with the mind you that there is a ton of fake 4K cameras out there )
The viofo A 119 mini 2 dashcam, look to be a excellent 1440p system.