if you know how to access the service mode, you can check the 2nd btr life in the HFSI.
Personally for me, they last about 200k/300k of the supposed life. You start getting streaks eventually, but you can also mitigate this to some extent by cleaning the 2nd btr with a damp microfiber cloth (water ONLY, do NOT use alcohol or it will strip the coating). The new 2nd btrs are getting better and better though. If you check on the guide plate, it should have a "2.0" on it as opposed to the old ones