I've decided it would be good to see some discussion based purely on the RoBF. I'm seeing it referenced in many other threads and, more and more, strong teams are using it.
But instead of posing my opinion on the RoBF, I'm going to present a few facts and numbers to the community and then let the discussion commence.
First, let me give everyone a link to the Wiki page. Making sure to give everyone a quick link to exactly what the RoBF is!
The tattoo of RoBF has 10 or more tattoos over 6 million in level, only the RoS having as many. Though most other tattoos have at least 5. (The ToE, FF and IF are exceptions, sorely underrepresented in the world of large tattoos)
The 3rd largest tattoo in the game is a RoBF, with the largest being a Jiggy and the 2nd largest being an EF.
An interesting statistic is this: "Rune of Balrog Flame 236 $17,228,435 $-217,552 " 236 being the number of RoBFs in the game, $17,228,435 being the average NW and the last number is AVG price - NW.
The RoBF has the second largest average NW of ANY item in the game, only the Halidon familiar beating it (rather soundly, I may add, at Halidon Familiar 151 $29,305,692 $-1,147,685. However, keep in mind that the Halidon has not been around nearly as long. I would go so far as to put forth that there are many, many more RoBFs on lower characters, inflating the number in the game and therefore deflating the average NW of those in use.)
Now, to give a bit of... "real" numbers from the RoBF.
Against Mikel's King of Pain, holder of the game's largest RoBF, my defenseless (relatively little mitigation) minions receive between: Corpse burns from the flames surrounding Roxanne (2529743) and Corpse burns from the flames surrounding Roxanne (2237253). These numbers coiuld be found via the Wiki and simple division, but I wanted to put it in a battle situation.
The damage is relatively low, truthfully. Considering those numbers are the absolute highest an RoBF could ever hope for, and it must wait until melee and only attacks once per round, I can easily claim that every other form of direct damage would do more per round against a completely undefended target.
From the largest Jiggy in the game "Kano-san pulverized Tattoo of WoC 
Kano-san crushed Tattoo of WoC 
Kano-san pulverized Tattoo of WoC 
Kano-san pulverized Tattoo of WoC 
Kano-san crushed Tattoo of WoC "
A well known, weak hitting tattoo still outdamages it.
However, while the BASE damage is low, the RoBF's damage is totally indepedant of NW of items, or MPR distribution. That is to say, for a jiggy, or a halidon, or any damage dealer to deal damage, it needs MPR. It needs NW invested in it. The RoBF is a constant, the damage nearly predetermined by an opponent's AC level and the size of the RoBF.
Because the second big factor, is unlike most forms (if not all), the RoBF has only one way to be reduced. AC. All other sources of damage have direct counters, while the ROBF lacks that. But is that a flaw, considering how low the initial damage is?
We've addressed the damage, but let's not forget the defensive portions of the tattoo. An innate, if low, evasion. The largest not even yielding 1.2 million levels in Evasion. This would be, if the chart in the Wiki is correct, (114) 1,173,096 from the largest tattoo in the game.
This, combined with anywhere from 20-30%, the largest the tattoo the higher up in that range of magic mitigation, and you have an all around tattoo. Physical and magical defense, with a source of damage that is difficult to mitigate.
For a bit of "real world" data, at the current time of posting, there are 7 RoBF in the top 25 characters (Score based.) The second in the top 25 is RoS at 5 (I would point out that the majority of RoBF are coming in closer to the top of the list, just to save people the trouble of looking, while RoS are closer to the bottom. But that could just as easily be MPR related.)
However, there are only 9 in the top 50. That's right. Only 2 between 25-50. This lack of RoBF further down could mean a variety of things. Perhaps the RoBF needs a large MPR to work properly. Perhaps only the most competitive players use it, or perhaps it takes USD investment in the strategy. Or maybe it just doesn't level well. Regardless, those are the numbers.
So those are the facts I've garnered for this discussion. I hope the community makes use of them to hold the discussion, and I definitely hope more facts are found by others.
May the debate on the Rune of Balrog Flame commence!