Lesse, it's actually a bit hard to tell since it's an LA rather than RHD (which was a different plan, 2 RHD and no LA). Flump Swordsage 1 since it was called out.
Level 2: All things being even they'd have an attack bonus of +0, +3 with a feat. No AC bump yet. The hover doesn't translate into any kind of advantage yet, and won't until level 4 when they can hover 15 ft in the air and can potentially use a polearm or ranged weapon and jab people out of reach of melee. Level 4 is the realm of Levitate spells, so that's already a tactic. Hp is squishy, but not dramatically so at an 8 vs 16s others might be packing. Less of a change if you're not doing max hp. LA isn't high enough for saves and skills to be too much behind either, just a bit. It comes with AC 18 so it's set armor-wise. (Note: If this is a problem an easy work around is scaling the natural armor. I'll consider it for later.)
They have 1st level maneuvers challenging actions with their stench, and manufactured weapons challenging actions with natural.
On maneuvers I suppose it depends which ones you use, but I believe a 20 ft line save vs sickened seems reasonable for a 1st level effect you'd fine at this level. Actually I believe warlocks have an essence for precisely that. Remember the nausea option provokes, its range is only 5 ft and that's still a ranged attack. At these levels with the hampered hp I'd consider it too risky to use. As far as practical applications, I can think of plenty of times where a maneuver is a better answer than using stench. Oh, this is completely unscientific, I'm just running through a few random situations I've encountered in my head and I just don't think sickening is all that useful unless you're working on that debuff and/or with allies.
On weaponry, it's 3d4 over time vs a weapon damage die. Here, the natural weapon is clearly superior. It's effectively a scythe (1d4 bludgeoning, 1d4 acid) with lingering 1d4. That's pretty neat. I expect utility to drop dramatically once magic weapons and/or iterative attacks come into play. A good example of the usefulness of maneuvers over stench can be shown here, I'd rather two stings via a maneuver than one stench.
On hover, as implied before it doesn't provide any benefit until level 4 because a monster with 5 ft reach can still hit you at ground level and 5 ft in the air.
The bardic lore I consider a non-power. It's too circumstantial to be useful for anything not revolving around elder evils, where they should shine anyway. That, and it's a skill check that isn't stronger than skill checks of those around them.
Comparing it to level to characters of other classes, the level 2s have more hp, with a negligible bonus in saves, skills, and BAB. Both are using level 1 maneuvers or spells or the like, so no power difference there. It has good AC, and is unlikely to be investing in any armor because of it. It could, but at this level with funds still a bit tight it probably isn't worth it.
Try Level 7 when the thing fully awakens at 6 HD.
It's been levitating since 4th, and 3 levels later it can fly. By this time others should be getting their wings, and the wizard has had his four two levels. The warlock got his perma-wings a level ago, so this seems about the right time for it. Speed is slow, but perfect maneuverability is nice. I can't say it's broken at this level.
With light armor, Dex, and Wis to AC it can be expected to be a good +5 AC above the crowd. This is large enough to make a difference, but small enough not to shatter the RNG. They'll be good front liners to make up for a lack of DR or that extra hp, which is now less of a problem now that there are more HD involved.
Stench spray continues to be useful but increasing less so as they get better and better maneuvers. They can get away with the nausea spray more, but I wonder if their DCs will keep up. Most don't dedicate Con, it's usually a secondary stat to whatever their class main stat is, so I expect DCs to start trailing behind. It's probably still pretty good here, but I don't think it'll keep up.
The natural weapon should be falling behind in power at this level because natural weapons are tough to enhance and they only have one. Its split damage will be doing it no service as resistances appear.
Compared to other classes... well, wizards are being wizards with 4th level spells, maybe something less extreme. 4th level maneuvers. On this odd level the flump is disadvantaged at 3rd level. It's less of a gap, but a gap anyway. This is.... tough to tell, it really depends on what maneuvers are in use.
I dunno. Looking at it, things don't seem too bad. I could stagger the natural armor so AC isn't so high to begin with, and AC usually lags behind attack bonuses anyway so it's not much of an issue in my eyes. The strongest ability out of all of these I find is the natural attack's high potential damage.
I didn't consider spellcasting. DC-wise, it's a +2 DC advantage or +1 DC advantage vs a +2 Wis race, for a 10% or 5% greater chance. I am unsure how much that affects things. I could consider the 2 RHD option too. That would bone spellcasters more, which isn't a bad thing.