I have never made a bad flare with this tool, they have all came out perfect. I don't think it works with stainless though. They appear out of stock, but Amazon has many of the same style.
[URL]https://www.eastwood.com/eastwood-on-car-flaring-tool-for-3-16-tubing.html[/URL]
I also use this to clean up and square the ends before I flare them.
[URL]https://www.eastwood.com/eastwood-tubing-deburring-tool.html[/URL]