Disclosure... I have been on Android for years before switching to the 6s+ this year. Overall, a mixed experience. I do miss some Android functionality (especially, my ability to format devices at will - more on this below), but the Apple camera and battery experience more than makes up for that. If only they could release something like the LG G4 using vanilla Android... oh, well. Having said that, I agree with the AT review of the Apple 6s and 6s+... the editor's choice is well deserved because there are a lot of things on Apple that "just" work. The SOC engineering is commendable and it does set a benchmark for Android makers to follow for years.
Anyway first things first: if you haven't JB'd yet, I believe you may be out of luck, but you can still try to JB. Also, if you have upgraded to 9.1, you're definitely out of luck because there's no JB for 9.1 yet.
If you're still on 9.0.2 , the Pangu JB may work on your device that has all your customized apps/settings, but people have had issues. Pangu recommends that you start with a "fresh" install of iOS. A fresh install forces you to check in with the Apple mothership servers... and here's the shitty part. Apple stops signing old versions of iOS a few weeks after every new iteration of iOS is released. Since it's been a few weeks since 9.1 was released, they have already stopped signing the 9.0.2 images. This means that you cannot "downgrade" to 9.0.2 even though you may be able to find a 9.0.2 image on the web.
So, if you're on 9.0.2, you can try to JB without resetting your device. Pangu may encounter errors, in which case, you'd simply do a restore from iTunes. This also means that you'll be upgraded to 9.1 and will have to wait for someone to JB 9.1.
Assuming you can (or are able to JB), here's my take on it. It's nothing more than a fancy way of adding UI-related tweaks to iOS. There are a gazillion tweaks (and most of them fucking themes LOL) if you JB, but you will need to do your research. The three JB tweaks that I have on my phone are CClean, CCSettings, and Filza (file system explorer). Filza is the most useful since it gives you access to the file system.
If I had to sum up the JB functionality (I'm sure this may offend some die hard JB fans/contributors... and my opinion may change depending based on my future JB experience), I'd say don't do it. If you're like me and miss the file system, then that may be reason alone to JB. However, if you never utilize the file system, you wouldn't be missing out on much. There have been tweaks on older iOS versions that add widgets to the iOS UI, but nothing like that is available yet on 9.0.2 JB.
* Excuse any typos.