Challenges Mode in Urban Trial Freestyle features five additional tracks. In this mode, gameplay on each track is based on twisted mechanisms, and totally different goals to achieve. The key factor here is that you use the skills that you acquired in the Stunt & Time Attack modes, but in totally different and twisted conditions.
Both versions of Urban Trial Freestyle feature the same proprietary physics engine (called Elephant Engine), so in terms of being a trial biking experience, PS Vita and PS3 are quite similar. Both platforms also feature the same game modes, outfits and motorbike customization.