Well, I'll give you a quick opinion... You say you're not willing to look at alternatives. BUT, I think I can make a case for it...
Here in Alberta anyways, you can buy a R12 replacement called R12a very easily, and cheaper than R134a. It's about half the price. It has a larger molecule than R134a, and also runs colder at lower pressures. By lower pressure, we're talking about half the pressure of R134a.
Also, you apparently don't have to vacuum the system to almost nothing either. 10 in hg is enough according to the manufacturer. They guarantee that it's noncorrosive. Something R134a cannot claim.
Also, if there is a leak in the system, You can buy one of their 2 stop leak products. One is for rubber, and the other is for metal. I know many people who use it in their vehicles here, and it works quite well, in one case, a tractor of ours was leaking down every week. We put the stop leak in, and it's been 3 years since we filled the system. It still blows really cold.
Redtec and duracool are two companies that make R12a. It's completely compatible with the R12 system, and the oil used in there.
Because I couldn't get the small cans of R134a ANYWHERE around here, I sucked the R134a out of the system and put in Duracool R12a. I can buy that stuff at the local family owned hardware store. Every machine dealer, mechanic's supply, and parts counter around here has it. Even Walmart sells it.....
If you want R134a, you have to take a test and wait 2 weeks for a license, and then you get to buy a 30 lb cylinder. So, if you want to take your AC refills to the mechanic shop every time (and if it's leaking, it will be more and more often), I would just use R12a and be done with the whole mess.

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