They work. I've used a sieve with the middle poke up to allow pellets in a snake to do beef ribs in the family q.
I can't see solid fuel bbqs being banned any time soon.
I use one as pictured above the square / oblong one.
I use it when making bacon, as I use a tiny piece of charcoal for heat, and to make the smoke.
It is what I first learned about smoking with, long before I found out about the Kamado /Primo and using charcoal.
I use it now, when I cannot use charcoal, such as when I am camping and using my small gas BBQ, or there is total fire bans.
So yes, i consider them essential, and will continue to use them, when the occasion arises that it is needed.