I don't understand everyone lamenting the loss of the add a bag thing on Rimowa bags. I never liked it, found it clumsy, never attached well, and with a 4 wheel design it was completely unnecessary. I just bought my third Rimowa carryon, first two are the Topas and just bought an original in the Cabin S size. With the addition of a personal item, I can carry a week's worth of clothes in the Cabin S bag, and I can do two weeks in my Cabin L bag.
My personal item sits nicely on top of my bag and attaches to the retractable handle and have literally never used the add a bag thing.
Additionally if you really want a Topas with the add-a-bag, go on eBay and there are tons available from brand new at or below retail to ones that have been used once or twice that are several hundred below US retail. If you can swing it while traveling, buy one in Europe. They're considerably less expensive there.
I picked up my first one retail while on vacation. Other two I've purchased have been pristine bags from eBay for $350-$500 less than retail.
Final note, Mr Clean magic eraser works MAGIC on the body and trim of your Rimowa aluminum bags. It can get minor scuffs and scrapes to disappear.