roguesw: personally, i dislike the flat sides because they're there purely for aesthetic, not practical reasons. the flat sides makes for an odd grip, and it removes even more knurling from the body, and most people already find the older round 6P slippery at times. the only advantage i can think of is that it would be slightly lighter, but i don't think its worth it in view of the disadvantages i mentioned. the hex bezel and LOTC is useful though
if you're looking to buy a 2-cell surefire and use it as it is, you should look at the other models surefire offers, and if possible buy one with combat o-rings like the Z2 or C2/M2.
in any case, your best bet is to handle it in person and see how you like it, because some people don't mind it. just remember that when it gets wet, it'll get slippery and that's when the straight body and smooth flat sides become an inconvenience that can result in you dropping the light. if you decide you still want a straight-body, you can get an old 6P with the round barrel, then exchange the round bezel and non-LOTC with surefire for a hex bezel and LOTC.
hope that helped