I recently purchased the 2-wheel Expanse carryon and won't be packing it until next week, so I can't give an opinion on how it does on a trip, but I know that when we did the Venice, Florence, Rome tour and the terrain we walked with luggage at times, I would have been concerned with the smaller spinner wheels. Depending on if you're doing a tour, checking your bag, etc. I would think that having two bags with wheels might be difficult to handle even if one does fit on the other piece of luggage. When we were in Venice, we had to carry our luggage up and down some hotel stairs and also bridges, so I frequently had to pull my personal item off the handle of my roller carryon. It was an over-the-shoulder bag, but it was fairly heavy. It was manageable, but cumbersome as I'm quite short.
For what it's worth, I'm trying a new approach this year for the Spain tour. I plan to take the new Expanse 2-wheel carryon, and my personal item will be a Lo & Sons Hanover backpack (I am not affiliated in any way). I haven't used the backpack yet, so I can't give an opinion on that either. I wanted a backpack with the luggage strap that was primarily one large open area instead of tons of pockets, would fit under the seat, and was light weight. The Hanover seemed to fulfill my wishes, so I'm giving it a try. My personal item is primarily small camera gear, electronics, and my "on the plane" requirements.