Sorry can't help you on a comparison, but I can tell you a bit about Prozinc. Have you checked out the website at
http://www.prozinc.us ? It is very informative, especially if you are just starting this new journey (videos, FAQ's etc).
As you may know, Prozinc is pretty new. It came out in November so not a ton of folks here use it yet.
It was created for cats only and works similarly to PZI. I'm pretty sure the web site and vet studies describe a gentle insulin, with 2 hours onset, and >12 hr duration, with peak action around +7 hours. One thing you will learn in a hurry however, is that doesn't mean it will act exactly like that in your kitty. Most kitties on prozinc get shots 2x/day.
I like it, but I have never used either of the L's. It is much better for us than Vetsulin was.
Newbie Advice you will get a lot here:
1.) Learn to test kitty's glucose at home with a human glucometer, (just like a human diabetic does) If you read other posts here you will definitely see why this is SO IMPORTANT. Lots of us will be glad to help. VERY IMPORTANT
2) If you
haven't started insulin yet, you would be smart to research LOW CARB food choices before you start insulin, and then recheck his blood glucose at home. Food choices make a huge impact on BG and this will affect how much insulin is appropriate. Do not change things blindly without knowing how to test the BG yourself. Changing food after you start insulin should only be done if you are testing BG, and are home to respond to a very low BG (hypo). In general, you will do best avoiding all dry food, but there is a lot more than that, go read...
3) Before you start insulin, it would be smart to post about your vets instructions, to run it past some of the old timers here.
4) come back with questions- you will have them! ;-)