"Electrician's Box Sinker" devices (e.g. Screwfix d74206 / d91913) any
good?

After hand chiselling about half the sockets in my house I started to
seriously consider one.
Thought about it, but someone suggested this to me one day, and it works for
me.
If you have a 110m core drill (cheap £20 type) sink this to box depth then
knock out the core.
Two holes like a venn diagram for a 2 gang box. Less dust than the box
sinker as the core normally stays intact.
I thought the hand method was neater, I could fix a box without breakout
around the edges most times, but seeing as you've got to plaster the
trunking anyway you may as well plaster round the box.

Toby.