I can speak for the newer MZ5(technically Mazda Mazda5 haha). The rated 22/28 is accurate. I have seen MPG in the teens driving it super short distances around town when driven aggressively short distance(not me) or moving items or shuttling people. But it is capable of low 30's at highway speeds(55MPH). The older ones have the 2.3L MZR. I have the 2012 with the 2.5L MZR. It is basically the same engine/transmission as in the Mazda3 S trims. MT is only on the base Sport trim and super rare. But it is the only Mini-van with a 6 speed standard. If you find one cheap enough or with a bad transmission there might be an advantage to swapping in the Mazdaspeed3 transmission.
The one issue I always seem to have is cargo room with 6 passengers. We're used to fitting snugly as it is but we typically have to stuff backpacks and other cargo inbetween the middle seats and all along the floor. I have moved sofas, dressers, and desks with it. And we have made overnight trips with 6 people. When hauling furniture I usually have to leave the rear hatch open and tie it down with a cargo strap. I've looked into getting a tow hitch since it could really come in handy. It would look really nice with a drop, pizzapans, tint, antenna delete, hatch spoiler, and LRR summer tires. Many of the Mazdaspeed3 or regular Mazda3 parts swap right over so I have looked at used parts for things like sway bars and exhaust.
I pumped up the tires to 40 PSI and holy Carp is the handling good, for a mini-van.
