Actually, doing i in recovery is MUCH safer.
If it's a bad image it simply will not install, usually. This is true for either method, however you will get a notice in terminal. As for typos, it will either work, or it will not. If you misspell anything, it will simply error out and not flash anything.
So far dead heat right?
Flashgui works... For now. What happens on the next update? The terminal method is foolproof, it ALWAYS works, unless there is something wrong, and then it simply will not. There is no risk, no fear of someone else changing something.
You guys sometimes may think doing some of this the old way is silly, but my phone is older, been flashed more and done things you haven't even dreamed of, yet still runs fine, and it is because of doing this stuff the right way as opposed to the easy way is why.