I've bought Big Stubby 3,00 picks because I wanted to have the hardest pick possible for maximum control and to try something new.
They are thick and hard, which gives a lot of control over your playing. On the other hand, they have these indents that make it uncomfortable to holdit between your thumb and the side of your index finger. Also, they're pretty slippery, which combined with their hardness and uncomfortable grip makes them pretty easy to be dropped while playing.
Also, I found that when playing my electric guitar on the clean channel, they made a certain, pretty unpleasant noise when hitting strings. It may be because of a material or shape different than my other picks, but I just didn't like it.
Even though, I think it's possible to get used to them. It's just not a pick for me.