Interesting. I was researching this very yeast/Brett pack this weekend. In the end I decided to go with 3787, and then add some Brett separately in secondary, which will be in the keg. For the following reasons.
1: 3789 is limited edition. If I develop a recipe I like and then can't get the ingredients I will need to start over.
2: Brett is "the beast". It is one punker of a bug and it can, and has, taken over breweries. Most brewers that try to keep it contained use separate buckets, siphons etc etc and label then "B". By pitching it separate in the keg I will only have one item to quarantine, and a steel one at that. Easier to keep sanitized. Plus, I'll probably have some Brett beer in the mill all the time anyway. LOVE the flavor.
3: Unless you are willing to buy a lot of smack packs, if you make any kind of good sized beer you will need to do a starter. I wasn't sure how the cocktail would react to that. Also, more contamination potential. And finally, I like repitching yeast cakes, and if I keep the cake pure ale yeast I, again, don't have to worry about the Brett.