RT-AC1750 B1 or RT-AC1900P for AIMesh node?

[chai-kung]

I'm currently using RT-AC88U and want to use AIMesh system so I look in the market for the cheaper way to make it work and come across these 2 models which are

RT-AC1750 B1 for $73 (not sure if this is RT-AC66U B1 upgrade? what differences in performance? Does it compatible with Merlin firmware?)
RT-AC1900P for $100 (again is this a RT-AC68U upgrade?)

Do I should go for 2xRT-AC1750 B1 for add more range with stable 5G network or just 1xRT-AC1900P equally in coverage?

What differences between "superior AC performance" and "Ultimate AC performance" as stated in the website, does it really coverage much larger area or it just a marketing hype?

Thanks.

 

[Grisu]

coverage would be the same, RT-AC1750 B1 is an RT-AC66U B1.
Mostly same hardware as RT-AC68U, RT-AC1900P got only faster clock rate and slightly newer chips.

They all use identical firmware!
I would take the cheap _B1.