The TB is slightly longer, so some tech-types here will probably have thoughts on longer barrel / better trajectory / velocity.
It is a factor on places like Canada, where a barrel has to be a certain length minimum.
Downside? You need to be sure you don't lose the thread protector, otherwise the threads will be banged up, and the added value of the TB will be lost. Also, depending on how the protector is fitted, you may have a bit more lead / powder buildup at that point (I have different barrels for one pistol, and see a difference in cleaning between them).
Also, in states where things are abusively regulated, a TB may be illegal (??) to begin with, so it may not be the best pistol for a car gun if you travel a lot.
I'm sure there are other factors. These are just off the cuff.