I brought home an American Brittany pup over the weekend. Talk about energy, the pup is only 7.5 weeks old and he can jump out of the playpen I bought for him. I had to get some cardboard to make a makeshift roof so he won't get himself into trouble while I'm at work. This evening we went on a jog and he lead the way for over a quarter mile.
If you get a Brit, be ready for a very energetic dog. Also make sure you puppy proof your house. As I said, I keep mine a a baby's playpen while I'm out. It gives him room to move around but it keeps him safe so he doesn't do anything that could get him hurt or damage my house. When he gets a bit bigger I'm going to build him a dog run in the backyard.
I'm glad the breeder gave me all the good advice about preperations for this dog. If I didn't have that playpen, that dog would have either destroyed my house or gotten himself killed. I've found him chewing electric cords twice already.
As for a comparison between the French and American Brits, I'm not sure. I wanted to look into the French Brits but couldn't find any breeders on this side of the country.