I was wondering if anyone had experience checking in trunk-style luggage on UA, as well as aluminum luggage?

1) Trunk style luggage - do check in agents immediately get suspicious of the size as not conforming to the maximum given its odd shape?
I was having this conversation with a Tumi sales person and I asked why they discontinued their polycarbonate trunk luggage in the USA and Japan, yet it is still on sale in Europe. She said she thinks that American carriers are not familiar with the shape and that problems arise when checking. Hence it was not popular. (Doesn't make sense - they still offer an aluminum trunk!). Anyway, have some of you traveled with this type of luggage and have any agents given you a hard time with them?

2) Aluminum luggage - does UA do a pretty good job destroying them? LOL
I have two Tumi aluminum luggages. They survived 4 longhauls on DL, although all pre-covid and in business class. They did get dented but thankfully not on the frame/ lip. I know the small dents do add "character." Haven't used them since. Only because I prefer lighter luggage. But I am curious how UA treats them. I heard that some time back, LH and CX would take care loading them on to the aircraft.