This dictionary has turned out to be the most used app on my iPhone. I read a variety of materials and Collins has rarely disappointed me. Everything is fast, snappy, the app loads up instantly. There is a very plain-looking user interface but loads of functionality.
Everything works without a need for internet connection including the pronunciation, which are provided for both English and Spanish. Hyperlinks are embedded into every word, so you can tap on one, whether it is inflected or not, and it will take you to the entrys page. You can look up verbs in their infinitive or conjugated form. It doesnt matter because the dictionary will recognize them all. Full verb conjugation charts are provided for every verb. This makes it great for beginners who need constant reference to verb conjugations as well as for advanced students who need to be reminded of the conjugations for some of the more exotic or rare verbs - although in this respect the conjugations dont always seem to be accurate. The verb "asir" shows "aso" as the first person singular yet if you look up "asgo" in the search bar, it will clearly refer you back to "asir". So my advice is not to put your complete faith in this tool for other than the essential and common verbs.
What I like about Collins is that instead of listing a bunch of translations for a given word, as many concise dictionaries do, it actually tells you the different nuances of the word, helping you to distinguish in what cases to use each one. For example, if you want to say "flat nose", youll see that the Spanish word for flat is "plano", but of course you wouldnt say "nariz plana" but "nariz chata", which Collins makes clear. In many entries there are loads of example sentences, all marked in blue for easy viewing, in order to clearly illustrate usage in case a mere translation does not suffice.
Among the really cool search features are the ability to filter only English or Spanish results, or both if you want. If youre looking up a word like "frugal", which is the same spelling in English as in Spanish, this really comes in handy to take away from unnecessarily cluttered or confusing search results. The ability to browse words from the ending also exists. Im not sure if this feature ever came in handy for me, though. More importantly you can search examples. Great feature if you want to search for an idiom of a certain verb, say "poner", instead of having to scroll through the myriads of examples to get to the one you want, you can just type it in and press enter.
If there was one thing to criticize, it is that the screen space is not optimized for the iPad. It only looks like a blown up phone app. The search bar is tiny and located in the very top, which makes it uncomfortable to use when the screen is so big.
If youre an advanced student and you are looking for a good dictionary for the iOS platform, you have a few choices. This one is my recommendation. Its expensive and there are very cheap or free dictionaries out there but dont expect to get premium content without paying for it or using ad-supported software. Ive also tried Word Magic Unabridged, which costs about the same as this one but I dont like it because of its confusing and overwhelming interface. Just my preference though.