It's not for me or my kids. We don't have any sensory issues etc. to worry about and we've just never done it. My kids are not allowed to run around wild at restaurants/pubs. We used to take a quiet toy, pencils and colouring in books when they were little...but now they are just part of the conversation. If we're in a big group they talk to their friends. Last year we went out for a friend's birthday to a restaurant...about 20 couples plus all the kids (lots of kids!...around 40). We had two loooonnnggggg tables set up. The adults all sat on one table, the kids all sat on another table. Not a device in sight. Kids and adults had fun, and kids were well behaved the whole time.
If they get bored...so be it. Boredom is a part of life, they need to get used to it.
Side note: We went out to adult events a lot as kids...and we were expected to sit at the table the whole time. My parent's were very strict on it. Perhaps this is why I figure my kids can behave in restaurants without needing electronics to cure their boredom...because it was expected of me as a child? I am pretty old fashioned, though...our electronic time is restricted at home, too.