If you're already willing to consider the sort of price range into which the JL Audio Fathom F112 falls, then you have many options for sure!
Given that you seem focused on obtaining a smaller size and nice aesthetics as well as lots of "punch", a high-powered, sealed sub certainly does seem like your best bet.
Right away, I would definitely recommend that you consider the relatively new SVSound SB13-Plus. I have been extremely impressed with SVSound's new "Sledge" amplifiers and the 13-Plus driver is essentially the same design as SVSound's 13-Ultra driver, which is rather spectacular.
Given that you have room in the budget, you'll also want to consider the "traditional" route though. Definitely take a look at Velodyne's newer DD PLUS subs - either the 12" or 15" model should fit the smaller size profile that you are looking for.
There's no question that the JL Audio Fathom F112 is excellent. If it's easily affordable for you, you should have zero qualms in wondering about its performance capabilities. I'm merely giving you a couple of options - one that is somewhat close in price (Velodyne DD+) and one that is considerably lower (SVSound SB13-Plus).
The sheer power, output capabilities and extension of these three contenders trump anything you're going to find from Rythmik, Epik or HSU in this sort of "smaller size" realm. Outside of the basics though, the DD+ and SB13-Plus also offer a tremendous amount of processing and options that other subwoofers just do not.
For me, the SVSound SB13-Plus stands out as the absolute "dollar-for-dollar" winner. In fact, due to the price differential, you could easily afford a pair of SB13-Plus, which will naturally offer greater benefits than any single subwoofer.
Hope that helps!