If your main concern driving the AP2.5 decision is with MCU1 vs MCU2 as stated, make sure the AP2.5 unit has MCU2. AP2.5 came out a number of months before MCU2, so AP2.5 doesn't guarantee MCU2.
Correct. AP2.5 came out August 2017. MCU2 came out March 2018. All AP2 or AP2.5 with MCU1 can be upgraded to the AP3/MCU2 combination.
The only place where there's really no meaningful upside to MCU2 upgrade is if you have AP1 hardware. It literally just gives you some games, faster processing/responsive screen and Netflix, best I can tell.