We can't answer worth for you - if you have a need for the particular small form factor that is the unique selling point of the x51 then yes, it's worth it. If you don't have a need for it and can consider normal desktops then it's probably not worth it, in that you can buy a desktop system that will be better for gaming, for less. Chillblast make pretty good systems, as do ScanXS or even Dell/Alienware desktops. Then you can build you own, which may save you money if you can't easily configure one of the above to match your requirements.
eg:
http://www.chillblast.com/Chillblast...dition-PC.html