* the way in which the phone switches between earpiece and speaker with VO active can be weird, you can lose focus on parts of the screen when on a call. it's much easier if you use headphones or choose to use the speaker manually rather than using the sensor.
* The rotor takes some practice, as does the optimum time to do a double-tap. The screen is very sensitive and that can be a bad thing on occasion.
* It's easy to accidentally magic tap (2 fingers twice), turn the speech off (3 fingers twice) or turn the screen curtain on (3 fingers 3 times). These gestures are all reversable by repeating them, but people panic if they grab at their screen and hear "speech off" and have no idea what to do.
* People also in my experience easily get lost in infinite scrolling lists: the calendar, photos, lists of social media posts etc. flick gestures are great, but learning some screen layout will be useful.
* the "z" back gesture can be hard for me, especially if I'm trying to do it in the hand in which i'm holding the phone. I have re-mapped this to a 2-finger flick down, because having VoiceOver read the screen from the top is never useful to me - I can put the cursor at the top with a single touch regardless. On the subject of re-mapping, a 2-finger left or right is also unmapped by default. it may be easier to re-map your rotor that way, move to previous/next container, spelling error, heading - whatever best suits itself to your use case. Some people even prefer to map them to top or bottom of screen, finding the default 4-finger taps awkward and extending the analagy that a single flick left/right moves you back or forward, 2 fingers moves you backmost and forwardmost.
* Gesture learning is invaluable (it's activated with space+k on a keyboard or a 4-finger double-tap). you can practice many of the gestures with this mode, except for the back one (which turns it off). Scrolling seemd like a pointless thing for me to learn as a blind person at first, until I realised that it saved me "scrolling over" multiple items singly.
* take the time to set up your typing feedback and typing style. These influence what you hear whilst you type and the method by which you enter text. Touchscreen typing has never been an enjoyable experience for me as a totally blind person who grew up with a qwerty keyboard and then a button phone but choosing the right input method takes a little pressure off. Braille Screen Input and Bluetooth keyboards are a useful extension if he's a Braillist or a typist, and ddictation has gotten quite accurate lately and can be triggerdwith a magic tap when a keyboard is visible.
* Also take a little time to look at the voices. You can use the same voice that Siri uses, which sounds higher quality to many ears, than the default default VoiceOver one. You can download higher quality versions of voices in settings, and don't need to be limited to your phone's base language for accent (i.e. you can use British English in the US, etc). you can also set up profiles so you have a different voice when reading in kindle, for instance, compared to reading in Mail.
* There's probably a tonne of things I've not thought about but hopefully this is a useful starting point.

Voiceover has its own bugs but overall it’s a good screen reader.

I work at a school for the blind. Most of my students prefer VoiceOver. The issue with Talkback deals with its angled gestures. VoiceOver is much easier to learn and master. If you do get an iPhone make sure to turn on the accessibility shortcut for VoiceOver.

Hmm, VoiceOver works just fine for me when I'm on a call and need to dial an extension. It helps to have Touch Typing mode on so you just have to drag your finger to the number on the screen and release to press it, plus have the accessibility option set that automatically switches to speakerphone once you move the phone away from your ear.

Ultimately, VoiceOver is just a much much better option overall. It will take a little getting used to when switching over, but the benefits of VoiceOver are all still lightyears ahead of where TalkBack is right now, even with the new version that Samsung released.

VoiceOver does work during phone calls. By default it even automatically switches to speakerphone so you can hear it properly when the proximity sensor detects that it's not close to your ear, a feature that annoys me whenever I have to hand the phone over to someone else as people think I switched to speakerphone on purpose so I have it disabled all the time. In addition, VoiceOver also switches to the keypad automatically so you don't have to do it yourself to navigate voice menus, but you can always switch back if you need any of the functions provided to sighted users by default such as switching to an AirPlay speaker,, muting the microphone, or starting a conference call.

One gesture you should absolutely be familiar with is Magic Touch, which is double-tapping the screen with two fingers. This gesture does a lot of things depending on the context, but the gist of it is that it either starts or stops things and is great for quickly answering calls without having to locate a button on the screen.

As for the comparison with Android, I'm absolutely clueless as I've never tried an Android device.

Would you like a gesture list with keyboard equivalents? I got the link eons ago on facebook, and I reference it sometimes when I'm using a bluetooth keyboard to this day. $1

As someone who came from non accessible phones, to windows mobile, to iPhone to android, back to iPhone for a month, and back to android I'd definitely say android is a quicker experience. I feel like I'm using a toy that is very slow and limiting when using iPhone. with the various gestures on android I can make calls, send and check emails, post on social media, and send a pic one handed before all my blindiphone using friends can respond to a text message. I just feel as if VoiceOver on iPhones though consistent and stable limits the user's navigation compared to talkback. Just me though.