I have no experience with flat rifle triggers either.
It seems to me that with a flat trigger, consistent placement of your finger might require more concentration.
Another way of looking at it is that you would have more options about finger placement, and could slide your finger down toward the tip of the trigger for more delicate control.
The front trigger on my Mauser's double-set trigger is European style, with a slight re-curve or bump toward the bottom. I have found this bump to be very useful for precision in pulling that trigger, which is just a few ounces when set.
I'd like to try a flat one out, someday.