R12 Refrigerant Quality Spi Brand?

[johnw991]

I charged my LS400 1990 with R12 Dupont from Pep Boys and the A/C now works great. I got certified on the web. I would like to get some R12 for future use at a reasonable price. I have a chance to buy 2 lb cans of virgin R12, brand SPI, on Ebay for about $14 a pound. Wondered if there is any difference in quality of SPI brand versus other brands.