Great question, and we have a lot of Sprint clients join BTD, even though there's a bit of overlap, and here's why.
The Sprint specifically covers how to create and design a Gateway Program, as well as how to price and sell it on autopilot.
While BTD has overlap in mapping out your program, it discusses creating ANY kind of program, plus how to actually run/deliver it.
So, Sprint is more focused on the sales aspect, while BTD is more about the client aspect.
If you want to know more details on how to actually run your program, show up for your clients, get them results, build your program, etc - then BTD is a good add-on to Sprint.