The advancement lines are kind of weird on this one. Maybe average salamanders were originally intended to have 7 HD?
These guys are small outsiders with 4 HD and stat boosts across the board. That said, they're a bit underwhelming mechanically. One natural weapon, the ability to add fire damage to attacks (as long as they're not made with nonmetallic weapons), and the fire subtype are all useful, but improved grab (limited by size, to boot) and constrict are simply awful on a small creature. The default flamebrother has a grapple modifier that about any 4th-level character would outdo, and as they increase in level things don't improve much.
Of course, they're not necessarily a bad option. A flamebrother could definitely be turned into a viable multiattacker; rogues for one effectively lose only one die of sneak attack damage if they build around Heat, and the natural attack further makes up for that.
Five more HD than the flamebrother. What does it net one?
Medium size, +2 strength (yes, that is the only stat boost compared to flamebrothers), a slightly stronger constrict (too bad the average monstrous grapple modifier got even higher over the course of those five levels), DR/magic, and that's it. The horrible speed doesn't get increased, no other ability scores do either, and even natural armor stays the same. -0.
It's a size increase and... could it be? Improvements to natural armor and stats other than strength! Heat and DR get upgraded a bit, as does Constrict, but that alone isn't worth the six additional HD these have over average salamanders. Fortunately, there's SLAs!
Nevermind; forget about the SLAs. The 3/day abilities are all bad fiery blasting, the 1/day abilities Dispel Magic (not even the greater version) and Summon Monster VII (which would almost be useful if you had any choice in what you summoned). -0, -0, -0 all the way.