Here is a good answer.
http://cheaperthandirt.com/blog/?p=4050
I've been watching this pistol for some time, and hope to own one in the near future. While it is certainly an amazing gun at a great price, It's no five seven. Below is a comparison of the 22mag Kel Tec vs 5.7x28 FN. For those that don't want to read the article it basically says the 22mag performs better in a longer rifle barrel, where the 5.7 is optimised for a shorter pistol barrel and produces over twice the energy of the 22mag when fired from a pistol.
http://www.thefirearmblog.com/blog/2009/11/23/myth-busting-22-magnum-vs-5-7x28mm/
Still the Kel Tec is going to be alot cheaper to buy and to feed, and alot easier to find ammo for.
Saw an article the other day in one of my gun magazines, that said .22 mag ammo designed for pistol length barrels will hit the market soon.