The damage bonus + power damage bonus gained through Hunter Mode/Fortificationis the selling point of the GS over the Vorcha. Without then you might as well go for the health regen coupled with the ability to self detonate fire explosions.
Best build to abuse Flamer is 5/6/6/4/4 or 5/6/6/3/5 (depending on whether you want a little more power damage or shield recharge rate).
5/6/6/5/4 or 6/6/6/5/3 have a tad more power damage than either of those. Geth have a built-in 10% shield recharge bonus, so eh. I can see the appeal of wanting to maximize it, but I'll leave that to flamer-less builds.
I went HM/Fortification, weapons have Geth. A true Geth Soldier. No flamer.
Flamer seemed so tacked on.
But if anyone's got any build ideas including a flamer, I'm always willing to promote and try 'em out.
The Geth Soldier can get a huge power bonus for Flamer. It will absolutely destroy armor and shields if you go with shield damage on Flamer's last evolution, which I would suggest. It's really fun to have a full power damage build with power damage equipment. Try it out one time. =o