What is the reason that you are taking Tuffy to the vet? Is this just a regular physical checkup, or is this to specifically address the diabetes? You are not the first to encounter resistance from the vet about home testing. I don't understand either, it's a safety protocol that human diabetics use, and directly applies to our pets also. It doesn't hurt anything, and it can help protect your cat from a hypo, or let you know if a hypo is happening so you can take action. You wouldn't try to build a house without the proper tools or plans, same difference. Testing is a valuable tool to help with the treatment plan.
Don't waste time feeling bad about shooting blind, you are not the first and will not be the last. You have now begun to educate yourself and Tuffy is going to be better for it.
You need the vet to prescribe the insulin, and to care for Tuffy if he gets an infection or gets hurt. The one unit you are shooting now may not be enough, post in the Prozinc forum, get more data for the experienced members to look at (more BG testing at different times of the day and night, when possible). You are right in increasing the dosage in small increments, so that you can see the effects when you test, real time and not overshoot the correct dose. Not via an infrequent test at the vet, which costs you more $$, with added vet stress for Tuffy.
Again, rely on advice from the experienced Prozinc users, they will review the testing data as you go forward, they have been doing this a long time and know what they are talking about. You are new to this new treatment plan, even though you have been giving Tuffy insulin for a year but the results of the last year have not been satisfactory. So, follow the lead of the Prozinc members, become more educated and be Tuffy's advocate and effective caretaker.
If you need to, get another vet that will work with you to get Tuffy regulated and healthier. It's tough to buck the system, but you are Tuffy's protector.