Those products are simply a way to throw your money away, IMHO.
The insulin you are using is helping to support the pancreas and let it heal.
A low carb diet will help keep the BG levels lower than a high carb diet.
Getting your cat to a normal weight will help with the BG levels also.
The home testing helps you to see in real time what is going on with your cats BG levels.
You are already doing what you need to do to help your cat.