:-?
New work boxes don't have ears...you need ears on old work boxes.
Old Work boxes don't have a side mount bracket...you need that bracket on new work.
I see 2 styles at a minimum.
How much is a 1G metal box (new work..$1.18 ?)....how much is a 1G plastic box( 0.52?) ?
A 4G metal box would cost you about $5 PLUS the labor assembling the thing.
A 4G plastic costs about $4.
Given the choice - why wouldn't you use plastic boxes?
I also prefer plastic old work boxes....they have a larger outside dimension than a metal box ....easier to get my hand in the wall....the metal box IS cheaper at about $1.43/per vs. the plastic at about $1.82 PLUS the larger device plate ~ BUT, if having the opening larger makes my job faster, I'm all over it