If you want to ride a stock bike I would say that the M.A.D Phase 1.3  is a better bike than the Tekiya and is around the same price.  The M.A.D Phase 1.3 has a front disc brake and is slightly shorter than the Tekiya so should be easier to learn on, also M.A.D are a well known trials brand whereas diamondback make many different sorts of bikes.  If you get the Phase 1.3 you may still want to buy a single speed kit as when learning, the derailleur will probably take some abuse and may break.  Hope I have helped.