It won't wear the trigger block , if it's a flat race ie three piece , they are designed so one piece stays still, it's the whole point of a thrust race.
As others have said the longevity of needle bearings would be my concern and I would feel a lot more confident using a plain bearing.
Delrin or Iglidur have low efficients of friction and should stand up pretty well.
I experimented with thrust bearings about 8 or so years ago.
I never really noticed an improvement over my usual setups.
If anything, as Nick says above, they pinch crucial spring room, so I stopped using them.
B.A.S.C. member
Another point worth considering, needle and other rolling element bearings aren't great with sudden accelerations, the angular momentum of the moving parts can result in them skidding instead of rolling. I don't know whether or not the movement of the spring end is fast enough to cause a problem, but it's something to bear in mind.