and then I will be done for a while, really!

I have a Sylvania breaker box, and need to put a common trip quad breaker in
for a new circuit because I am out of room. Two years ago I put in a
Siemens quad, so I know they fit and work; but now can't find one. I need a
C23030CT2. Lowes carries Murray, and while they don't have the one I need,
they have a quad that looks to be identical to the Siemens. Are they the
same? The Murray I need is a MP230230CT2, and seem to be readily available.

(I am tempted to pull out three circuits going to my workshop and put a
subpanel in, rather than putting in the fourth circuit. I sure wish I had
done it that way originally.)

I intend on running 10/2AC or 10/2MC. The AC is $0.60/ft, and the MC is
$1.10/ft. What about the MC is worth nearly twice the price? I don't want
to waste $50, but I "save" $50 by buying a product that will be much
inferior.
That's all, thanks.