There is little downside to having a catch can

 

A voided warranty might be one.

 

That's my concern..I have a 10 year 175,000 mile warranty that I paid big bucks for...Even now Ford is balking at replacing a defective air dam...

 

Then you should just stay away from any modification.

Honestly, the biggest risk is if you take your truck to the dealer for an engine related issue. They could try and prove that the issue was caused by the catch can you added. But just because you have a catch can installed they aren't going to deny warranty coverage on an unrelated system such as a transmission failure. A catch can is easy to add and remove. If you're that worried about it just remove it before taking it in to the dealership. It will leave no sign it was ever installed if it was installed properly.