I've never heard of one of these bits before, but I did some googling and I've copy/pasted a couple of Q&A's
'Lack of basic riding skills. The rider is too heavy handed and is unaware of correct pressure and release You only need to ride with light hands when using a Pee Wee ' Q. Why should I buy a Macs Equine Pee Wee bit ?
A. Because, not only does the Pee wee bit give amazing control requiring only light hands, it is extremely comfortable for your horse
Those are just two things I found, but it seems that it ISN'T a 'bit for all occasions' but more of a 'bit for those who can ride with consistently light contact'
I don't think it would be suitable for everyone, my horse would hate it since he likes to play with his snaffle, the rigidity (sp?) would drive him nuts!
I used one for a period of a couple of months. My horse rode fine in it, I I didn't notice any particular change when in the saddle. I did notice that he started clamping him teeth together when I went to put the bit in him mouth, something he'd never done.
Later I was told by an instructor at Pony Club that it wasn't a very nice bit, for reasons I don't remember (sorry!) and I switched to a oval-link snaffle which he likes much better. No more teeth-clamping.