Despite widespread complaints about Facebook Messenger when it first came out, more than 500 million people have now downloaded the app.

Originally, people could chat via the Facebook app on their phone, but Facebook opted to split that function into a separate app in July, forcing users to download a standalone application known as Messenger, according to PC Magazine.

The Messenger app has existed since 2011, but it wasn’t until Facebook eliminated the chat ability in its main app that people headed to it in droves. The change mainly affected iPhone and Android users; those with an iPad didn’t need to download Messenger. Facebook announced the move in April.

Facebook couched it as a success, noting that people were replying about 20 percent faster via Messenger than they had through the Facebook app. Messenger users can now get voice calls over Wi-Fi in U.S., Canada, and India, and the app also allows for the creation of groups and for message forwarding.

Facebook founder Mark Zuckerberg acknowledged that it was a “big ask” to get users to download another app, but he said he believed it would improve users’ experience with Facebook.

Facebook’s goal with Messenger is to provide an app that works better than simple text messaging by allowing for better sharing of photos and videos as well as group chats, while keeping the messenger up with technological trends through regular updates.

One feature includes the use of “chat heads,” which is when a friend’s message displays their profile picture even when you’re using a different app. The aim is to allow users to quickly and conveniently identify whether the message is one they want to handle right now or dismiss altogether with a quick swipe.

Smiley faces and stickers have also become more prevalent, and Messenger aims to take advantage of that with the Messenger app. It boasts downloadable sticker themes and a virtually endless list of options for expressing moods through text in ways that words can’t.

There’s also the fundamental concepts of speed and simplicity. Facebook wants Messenger to be a speedy app with a clean, simple interface. Freeing it from the Facebook app was essential to ensuring that, the company believes.

A final feature of Messenger is the option for voice calling. Messenger allows for free voice calls, although both you and the person you’re calling both have to have access to Wi-Fi at the moment. Otherwise, it goes to voicemail.

Chief complaints about Messenger when it was first forced upon users were numerous. Among them were prviacy complaints, as the app asks for detailed personal information. Users also reported that Messenger drains battery life due to constant notifications that need to be turned off and its need to run all the time. Some also complained that the “chat heads” pop-ups are annoying and distracting. The separate app further annoyed users by forcing to go to a different app on their phone to perform what they saw as a quintessential Facebook function and saw it as inconvenient.