I always think it depends on what you want and what you expect others to think.
The TBS helmet is good and affordable, but it needs modification to be 501st approved. Other helmets are going to be more accurate, but also more expensive. So if you’re looking for something accurate with no mods, it’s an easy decision to go secondary market; however, if you’re looking to just display a helmet, the TBS helmet works for that perfect.
I can guarantee outside of this forum, the vast majority of people who see either version will know it’s a stormtrooper helmet and that’s about it!