Since Jetpack is one of the most popular WordPress plugins – with an install base of at least 5 mio. – it makes total sense to offer an integration. Remember, Toolbar Extras tries to be as useful as possible for its users. And, the users come first, and not the question if a plugin might be “good” or “bad” in a more non-technical point of view …
Also, while I was starting to working on this integration I realized that a few of Jetpack’s admin screens were not accessible/ discoverable very easily. From this regard, it makes even more sense to offer an integration from the Toolbar to have users quickly get to those screens, for example the alternative Modules Listing and the Debugging Center. This saves a few clicks, plus some headaches. — Additionally, these pain points of Jetpack were already called out by users, so there seems a general need for this, too. If you want to see and use these improvements yourself, upgrade to Toolbar Extras version 1.4.2 or higher, or just try it out and install it for the first time :-).
Video Demo of Jetpack Support in Toolbar Extras
This all said, personally I have collected some reasons why the use of Jetpack is not recommended in general. Again, the vision and integration of the Jetpack plugin in Toolbar Extras and me personally not recommending its usage, are two completely different things.