I did all my brake and fuel lines in SS. non seamed, as a complete newb..... and I was shocked NONE of them leaked.
I used Rigid flare tool and what I did was clamp the line in the tool with my cut line on the back flat surface of the tool, then use a fine hacksaw to cut it flush with the flat side of the tool.... that gives you a nice 90 degree cut or damn close.....file it dead flat with the tool surface, then debur the inner edge..... then take the tube out, flip it around and flare
Everything I read was to avoid putting heat into the SS before you flare it.... hence the fine hack saw by hand at low "RPM" and a file.... no power tools.
Mine worked great.... I was kinda shocked since it was my first time at doing flares.
I did have a few goofs with not getting the bend quite right.... of forgetting to put the tube sleeve or nut on before flare
..... but none of the flares leaked on me