When you get right down to it, you’ve seen Google Duo before. Oh not Duo specifically, but things just like it: popular video calling apps such as Apple’s FaceTime or Microsoft’s Skype, or the see and be-seen calling capabilities built into Facebook Messenger or Snapchat.

Heck, Google even has its own Hangouts application.

But video calling has become a table stakes kind of feature and what Google is promising when the company starts rolling out Duo to the app stores on Tuesday morning is speed, simplicity, security and the ability to work across all sorts of network connections. The mobile app will be available globally in 78 languages, Google says.

Of course, since so many of us already typically rely on one video calling service or another, I’m not sure how many folks will give Duo a try, especially since it isn’t preloaded. According to Google, however, 46% of U.S. adults never make a video call on mobile, based on a recent company survey of online users 18 and older.

Duo is indeed simple to use but it’s also bare-boned—for example, it is not tied to an instant messenger app in which you can also text. Instead it’s all about letting you make or receive a video call from your Android or iOS phone with the added ability to make such calls across the rival platforms.

During my tests, I was able to successfully be part of calls made from my iPhone to Android phones and vice versa. The app is compatible with the Jelly Bean version of Android (or later) and with iOS 9 on the iPhone. It also worked on the iOS 10 beta.

Duo is a mobile-only service, at least for now, so what you cannot do is call a friend or colleague from or to a desktop PC or laptop, as is possible on Skype and FaceTime.

Both parties must have the Duo app, which you can grab for free from the App Store for the iPhone or the Google Play Store on Android. Google hasn’t made a decision yet on preloading Duo on Android phones, as is the case with Hangouts.

There’s not much setup involved: the service is phone number based so you can call anyone in your phonebook who has the app. But that also means it won’t work with Android tablets or the iPad.

Google promotes Duo in this YouTube video.

Google also plans to integrate Duo into its upcoming Allo messaging app, but Allo isn’t here yet and such integration hasn’t taken place.

As with other video calling apps, you can mute your voice. And you can see what you look like to the other person just as the other person can see you. As is also standard elsewhere, you can change camera views to focus not necessarily on your own mug but rather the environment around you.

A shortcut to initiating a call: you can tap on pictured circles representing contacts you recently spoke with.

Through Knock Knock you can get a video preview of a caller before you answer. (Photo: Google)

Duo does offer one potentially knock-out and novel feature called Knock Knock, which lets you see a live video preview of a person calling you before you answer. In that recent Google survey, one in six U.S. adults indicated that they don’t engage in video calls because they feel it is rude. Google hopes Knock Knock will make such calls feel more like an invitation rather than an interruption.

If you’re not in the mood to talk, the Knock Knock preview will disappear after 30 seconds and the call will disconnect. The caller won’t know that you intentionally ignored him or her. A caller cannot leave a voicemail.

On an Android phone you can see the Knock Knock video preview even from the lock screen; on iPhone, the Duo app must already be open for the person being called to see the preview. Most importantly, though, Knock Knock only works with someone in your contact list. Still, if you’re wigged out by the idea, you can turn the feature off.

You can also block callers you’d rather not hear from at all.

Duo, unlike Hangouts, is designed for one-to-one calls only, not group video chat.

During my tests from Android and iOS devices, both the video and audio quality of calls conformed to the quality of my network connection, excellent in a robust environment, less so when the connection was poky. Either way, I could seamlessly move from Wi-Fi to cellular and back without dropping the call, and Google claims that even on slow “2G” network speeds the video can degrade “gracefully.”

I’m not sure about that graceful part because when I faced a challenging network environment both the video and audio sometimes stuttered or was badly pixelated, and at its worst, momentarily froze or disappeared entirely. To be fair, this is not dissimilar to the experiences I’ve had in poor network environments while using Skype or FaceTime.

Meantime, during my testing period, the iOS version of the app crashed a few times. Google became aware of the problem and subsequently fixed it.

Google has hardly reinvented the video calling wheel with Duo, and if you already have a video calling favorite, there isn’t a huge incentive to switch. But Duo does offer one more easy way for folks to make such a call.