I own the 134 brush and have never used the 150. Based on the reviews i've read, the 150 doesn't seem to be that great. I think the reviews i've read say it's too coarse and sheds too much.
The 134 is paddle-shaped and is not your typical powder brush. It's still big and fluffy, but its paddle shapped. It was a bit awkward to use at first because of that reason, but now I really like it because it can get into small areas around the nose and mouth even though it's really big. It's also really soft and i've never had any shedding problems
I use it for loose powders, MSF natural, bronzers, and sometimes blush when i'm in a hurry. It's also great for applying Blot Powder