in a less patronising answer…
For child 1 and child 2 we had a summer infant video monitor.
Child 1 had a fairly basic one – just a single camera and monitor.
For child 2 we inherited a fancy one from the brother in law where you could remotely move the camera angle around and speak to them (totally pointless and not reassuring to child, but great for freaking them out when they’re messing around!). Could also link 2 cameras up and flick between them for multiple room monitoring.
The basic one would have done the job fine, but why not have added bling when it’s free?
In term of use, they were great for not rushing in to every little noise which just stops the child from settling by themselves and disturbs them when they may have been half asleep. It had a light thing that flashed up when there was a noise so you didn’t need to have it constantly on, just sat in the corner of the room. And at night it sat next to our bed on low volume so if there was noise you could again just check that they weren’t actually properly awake and didn’t need you to go rushing in and waking them up!
However, in between child 2 and child 3 we lost the screen charger and never bothered replacing it. But generally by the 3rd child you’ve realised they’re not going to do themselves much harm and only respond to bigger noises 😕
Also, that was 5 years ago and wireless tech / smartphones / wifi stuff has come on a lot since then so all info may be irrelavent.
Edit: Think the basic one was about £80 at the time. Fancy one was nearer £150.