I use it, but mainly as a guide for buying real paintings. If I need anything else I just go on the Animal Crossing wikia, it has more information than the app
I use the animal crossing new leaf guide. It's pretty good. It keeps me up to date with events, birthdays as well as bugs and fish to be caught and when and where they can be caught.
I used it for a little while, but I had to delete it because I was running out of room on my phone so I moved it over my iPod. I use it every so often.
I use the ACNL Guide on iOS. I really like it for collecting because it helps me check off what I've collected. You can also tap the pictures for additional information (like when is the best time to catch a fish/bug) but I'm not sure how accurate that is. It also lists villagers, events, PWP etc.
Yes! I used one that was in English, but then I switched to one in Spanish since it's the language I play the game in. The English one was so benefitial to me though, because I learned the name of many catches (deep sea creatures, bugs and fish), events, villagers... I only knew the Spanish name of.