I love Cricket and Talla!
As far as street dogs being good sport dogs, it depends on the individual. Most of them are built for it and have the intelligence and trainability to do most sports, but some don't have the edge to be flyball champions or super speedy agility stars. Honestly getting an older dog for sports is a good idea if you are getting a previously owned shelter dog, but with street dogs if you get an older dog, there's a **** good chance the dog's not going to have the proper socialization under its belt in order to make the change from street dog to sport dog. Most street dogs aren't treated very well by most of the people they encounter, and they learn to defend themselves against other dogs and prey on small animals. I would advise against a more mature street dog for a sport prospect, though they can make superb pets!
They're all individuals, despite having a common tendency towards cleverness and problem solving. For example, Talla was way more drivey, tuggy and fearless than Cricket was at the same age. They were both affectionate, friendly, confident puppies, but one was a complete land shark and the other a bit more stoic.
They are not a "breed" with a set in stone temperament defining them, so you get quite the variety. You also get quite the variety of ears, coats, colors and tails. What you usually do get set in stone is medium size (between 30-50lbs), tough feet, moderate and balanced structure, a strong jaw with a good scissor bite, and full dentition. They are usually relatively light in bone and built for a combination of speed and endurance.
They are territorial. All dogs are territorial, but Mexidogs are territorial enough for it to need mentioning. It's certainly less noticeable in females and in puppies that never lived on the street, but they are protective of their home and their people.