I haven't used a Flat 50, so I can't help from experience.  
I use a Nantucket bridge, in a non Tele guitar..  I have to go on memory, because it's been a while since I used the Boss (have Flat 52s in now), but the Boss and Nantucket, on paper, appear to be in the same general ballpark in terms of heat.   I can say that I get a more beefy sound out of the Nantucket.  I chalk it up to the nature of the types of pickups, that is, a P90 is ballsier than a Tele pickup when similar in output.  
 I haven't studied or made pickups, so...I may be full of it.