I personally will steamroll the aqua shadow missions, but I would say they are on par with the mission 12 or so stage 5 missions in difficulty. For most people, they will be do-able. For people who do not have .... ehh 550k TP I would guess... the last stages might be a bit hard.
The good thing about the last mission is, if you fail it you don't lose stamina as long as you haven't completed it before.
AKA, if you barely beat it by getting lucky, that is you indication to get another equipment slot, or another 50 or so ampies into the units before trying again (just to be sure).