I've done both venues and these are the differences I can think of off hand:
BH will be done in an open, grassy field without other dogs in close proximity as opposed to a small ring with lots of other dogs around. This is something to prepare for as dogs who are used to working in cramped quarters with a lot of stimulation can have trouble transitioning to an open area without a lot else going on, and vice versa of course.
BH both teams report into the judge. Similar to the meet and greet in the CGC.
Absolutely NO hand signals are allowed in the BH. And no "double commands". That means no stay commands, no using the dogs name in conjunction with the command, etc.. Handler must have both arms hanging naturally at the sides and swinging normally. Can't hold the left hand at the side as in AKC.
There are no "NQ"s in IPO as there are in AKC. Different faults result in different amounts of points off, but even a completely blown exercise doesn't automatically mean you go home with nothing as it does in AKC. Though you may not have enough points left to pass, no one fault can lead to failure in the obedience portion.
As Keith mentioned, the distances on everything from heeling to recall to how far the handler is away from the dog during the down stay are far greater and dog and handler need to be accustomed to that.
BH heeling is a set pattern which the handler is expected to have memorized, not called out by a judge. The pattern is much longer than in AKC. On the BH the pattern is done twice, once on lead and once off, and amounts for what seems like an eternity of heeling.
The about turns are completely different.
IPO(BH) heel position is a bit different from AKC, but that won't matter at the BH level.
BH has a sit in motion and down in motion, both out of heeling, which don't really exist in AKC so those would need to be trained.
Heeling is through a group of 4 rather than a figure 8 through 2 people, but is a similar pattern.
There are specific rules about when the leash goes on and off, when you can praise (only in basic position at the end of every exercise).
The long down (down stay) is done one dog at a time, rather than in a group. 2 teams will report in at the very beginning, one will do the field exercises while the other does the down, and then they switch. You will be much farther away from the dog on the down, with your back to the dog, and the down will last much longer since you're waiting for the other team to do their whole routine. At the BH that can amount to 10-15 minutes.
The traffic portion is much different from a CGC. For most of it, all of the dogs will be going at the same time, there will be groups of people, joggers, bikers, cars going by honking their horns, and an impartiality test where the dog will be left in a group of people, left tied to a tree while another dog is walked by, etc... The exact exercises vary from judge to judge, but those are the most common.
That's all I can think of for now... Best thing to do is to read the rules for the BH and then watch some videos so you can see the differences.
