I have all the apps for the I-Phone, they kinda suck! I have Dirrs, paid 14 bucks for it, its pretty cool I guess, but don't ever use it. I wanted that leaf snap for proving tree ID. HO's, from time to time, get confused on what tree they have, not wanting to insult their intelligence, thought this would be a good way to show them that they are wrong, with out pissen them off! To bad it hardly works! If you are getting them for ID, don't, they are not totally accurate. If you are trying to increase your ID skills, get a field guide and go to a big park, bye yourself and ID every tree. I did this several times, now I very rarely come across something I don't instantly know.
Your in So Cal, I did it at Balboa Park and Live Oak park in Fallbrook. Live Oak park has a immense amount of cool trees.