Is it worth to buy it or not?
It appears to be quite a good product, and it will depend on what you plan on using for a controller.
In my case, it would have been a lightweight digital piano (Yamaha P-95), and since the BK-7m has no pitch bend control via pedal, it isn't going to work for me.
However, it may be the ideal rig for you...it certainly sounds great in the demos; better than a G-70 or E-series in my opinion...improved detail in the styles especially. Plus, it will have lots of fresh new styles, and that's always a good thing.
Ian