Even if it is single one it makes a difference. When there are 2 of them (from different vendors) then they can play with MCU in quite complicated set.

More here
https://blog.coinkite.com/understanding-mk4-security-model/

And also if you prefer Guy’s read
https://fountain.fm/episode/5kdybDzg6HJHLxEajAyS 

 both SEs are vulnerable to laser fault injection and lack basic protections that has existed in any credit card for the last 15 years