This app is extremely useful when trying to breed any dragon, especially since you dont have to question whether or not you are using the right breeding combination - It gives peace of mind in that respect. My only complaint is that the breeding simulator is really only useful for seeing what dragon you might have gotten based on the breeding time, but even then some are identical anyway.
What would be more useful is to add what chance you have to get each dragon WITHIN the breeding simulator. I know you can see your chances in the description of the dragon, but that changes depending on how you bred it, and the list of breeding possibilities is so impossibly long that it is much to inconvenient to scroll through looking for yours.
Also there is the option to use the -20% time for the upgraded breeding cave, but no "increase chances of rare dragons" for the Epic Breeding Island, or for dragons that have a "slightly better" chance of breeding rare dragons because they are lvl 11 or higher. This would be more useful in conjunction with my last idea, but I think both would be easily implemented.
Aven7777777 about Breeding Guide for DragonVale, v1.8.4