There's nothing about TailsOS that could arouse suspicion if there's nothing persistent on it that could arouse suspicion, or draw more attention to you. TailsOS is strictly a utility like a wrench or a screwdriver. Providing you exit TailsOS properly and watch the screen as it's wiping the memory to ensure it has infact wiped. TailsOS can prove to be an innocuous O.S after you unload it from memory. They might ask questions, but they have nothing on you.

Bringing a Windows OS is stupid as Windows doesn't clean up properly after shutting down and leaves a forensic footprint which is difficult to cleanup unless you use something like Bleachbit[1] or CCleaner after using Windows. You typically want to offload cleaning up to the O.S level and avoid using such tools such as CCLeaner in the first place (Keep in mind, since this is Windows, there are issues with free space on the drive that leave deleted files remaining on the hard-disk, even after explicitly stating they should be deleted).

With TailsOS, In other words, you can browse freely and with peace of mind that you won't leave a forensic footprint behind, giving you an upper-hand over other passengers who have to self-censor their browsing for fear of scrutiny at a later date from border officers.

[1] https://www.bleachbit.org

[2] https://www.piriform.com/CCLEANER