What do you want? A track bike? Or a stunt bike?
They are two totally different machines.
The track bike need to be set up for exacting performance.
I won't go into it.
The bike in the link looks good as a starter track bike.
From the rear tire pic, looks like he never "rode" it.
You need to look at it in person. Take someone who knows bikes, & is not as excited as you are, with you.
They can spot trouble you would otherwise over look.
A stunt bike Need to be set up to be Busted up.
Big guards, Giant sprockets, Crappy suspension, Caved in tank, Tail bar,etc.
If you want a bike that is going to take you repeatedly into the 120+mph zone.
Get one that is going to do so reliably. One that is worth putting the expense into.
Any old bike will do for a stunter, as long as it runs.
Remember. These bikes were not designed for stunting.
They are made of metal. metal fatigues after so many repetitions. then it breaks.
(this could be you)
Stunting loads are not what the engineers had in mind.
So buy accordingly.