Great minds, Lissie. I recently bought that exact same bag.
At 19.5x16x8 inches, it's an odd shape for the typical 22x14x9 inch US airline standard, but its overall total numbers are within the limits. I took it to the Tucson airport and had the Delta folks look at it. They said it was okay. I wasn't as concerned about the sizer as I was about it fitting on edge in the overhead bin.
SOTL, you might do the same with your 3/4" over bag. If it's soft-sided and not stuffed to bulging, it would probably fit the sizer.
The weight is also an issue for me. I try to keep my "big" bag down to 22 pounds fully packed so I can lift it, carry it and maneuver it by myself anywhere. I weigh everything I plan to pack separately with my kitchen scale, then the full bag with my luggage scale. Too heavy? Something's got to go.
My biggest and heaviest bag is an older 22x14x9 inch soft-sided 45 L spinner that weighs about 6 pounds empty, according to my luggage scale. I don’t use it for any travel that involves planes or trains anymore.
My other bags are all 2-wheeled, range from 36 L to 41 L and are below 5 pounds empty. The Osprey like Lissie's weighs 4.5 pounds and is my lightest bag, but with a 38 L capacity, it's not the smallest.
As a solo traveler who has developed a light packing formula over time, I can't imagine managing a 25" bag, even if that does include the wheels and handle. And having sat in the back of a plane watching the checked bags being loaded on the conveyor belt, I avoid checking anything unless I absolutely can't avoid it.
You don't mention what the 25" bag's exact measurements are or what it weighs empty, but I'd guess it's much more than 5 pounds. That's not such a big deal until you fill it and have to lift it up a set of stairs or control it going down them, no matter how few there may be.
P.S. With a husband at home, 5 adult kids, their spouses and 14 grandkids, I stopped buying gifts in Europe a very long time ago. Makes the going home packing a lot easier. 😉