There's been a good amount of discussion on this. I think you'll find a fair number of happy riders with Gerbings, Aerostitch and Widder heated clothing.
I have both Gerbings and Aerostitch. Gerbings are great but they won't zip in the lining of your Darien jacket. Aerostitch also has a new vest out that inflates to offer a snug fit. Trick, but it won't zip into the out shell either. If you want to stick with your Darien jacket and a zip-in liner, use the standard Aerostitch.
Others like widder, and generally prefer them over the Gerbings because they offer reasonable heat with less power consumption--an issue for most of us on the FJR. If you're a newbie, suggest you add a datel voltmeter to monitor your loads. If '05 or earlier, you may also want to try an upgraded stator to give you a bit more juice for heated rides, especially if you have other farkles (accessory lighting in particular).