Wilbur--YES, Depo works well for us. My cat has the same thing your
cat does--linear granuloma-- plus asthma, so the Depo Medrol is a Godsend.
Be forwarned that you have to keep it to a minimum, because it increases
a kitty's susceptibility to diabetes. I believe Rhonda had a cat that got
diabetes after a single Depo shot. However, I have been giving Gracie
Depo shots for over three years, and she has no side effects. (I can't tell
you if it works better than any other treatment because  it is all we have
used.
I can tell you that she most she gets is four shots a year, and there are
some
years she has had only two. The vet says, more often than every two months
really increases the diabetes risk.

I am pretty sure she said "linear granuloma." This is the rare form
of Eosinophilic Granuloma, and is named this because the bumps
generally form in a line up the back on the legs. It sure does make
them lick--Gracie's legs are sometimes hairless in the back from this.
(To be safe I wait until I see a bump or hear that she had congestion
from her asthma to get her a shot.)

Given my experience, I would try the Depo shots first. Talk to your vet and
see what she says about the risks. And please come back and share it here,
who knows, she may know more than my vet.

They are all different. Gracie did the best on a low-grade flavor of
Fancy Feast called Chopped Grill Feast and Purina One dry. She only
needed two shots a year that year. I switched because I thought maybe
better quality food would be helpful, but may switch back. Good luck!

My Shamrock has had Depo shots nearly his entire life. The
dermatologist I took him to said they're mostly safe if given no
more than every 4 months. That cats metabolize steroids better than
humans and even dogs. That said, a cat that is at risk of diabetes
(genetics) can get it from steroids. Shamrock (4 years old) just
had a full blood panel, and so far his blood glucose is still in
the normal range.  I've read that oral steroids are safer because
they are short lived compared to Depo that takes much longer to be
metabolized. However, in our experience, oral steroids take much
longer to show any effect, where injectable Depo shows improvement
within a couple of days.

My Shamrock gets allergy shots because his inhalent allergies were
tested for, and a serum created to specifically address them.  
After nearly a year on the serum, it hasn't completely "cured" him.
The need for Depo has decreased in frequency, but all in all, I'd
say the allergy shots is a failure. It was an expensive "try" but
I'd do it again.  Now his dermatologist is recommending a drug by
Novartis called Atopica.  Atopica's label use is for dogs. Rarely
do people opt for this for dogs because the dogs that are mostly
genetically affected by allergies that cause skin erruptions are
big dogs, and Atopica dose is based on weight. It makes it too
expensive. Our dermatologist said that for Shamrock the first month
will be $80, then decreasing the dose until it reaches 1/2 of the
initial dose. $40 a month for life is worth it to me to keep him
comfortable.  Nothing else has worked.