Generally, in my experience, this is the best "deal" you can get without an outright dismissal, which is pretty rare. Trials are unpredictable. When you get a deal like this that doesn't require a plea, and ends up in a dismissal if you are a good boy, a trial is an unnecessary risk. Much less risk in committing to keeping your nose clean for a year than to have a panel of jurors and a judge who may be in a bad mood decide your fate. That's not to mention the publicity that this specific case would get. Also, DAs usually don't offer these types of deals to habitual offenders who aren't able to live up to the terms.