What's the difference exactly? The way it interacts with other forms of Double Attack? Meh. I'd be content with a straight +DA% like Fighter's Roll (except not random, obviously, since random strength buffs are COR specific -- it should be equivalent to a decent, but not perfect, roll).
For current content, though, it doesn't matter how it functions or even what the duration/recast/cost/%DA given is, it's still crap. The target can get tp faster, but only by feeding tp to the mob faster, which everyone hates and fears. (Even if the TP moves themselves aren't dangerous, it still screws with proc timing.) Most melees aren't meleeing most of the time anyway. Regain atma and just pop in to WS is much safer, especially on things with dangerous AOE.
If you didn't want the DRK in party to hit the mob once per round before, you certainly don't want them to hit the mob twice per round now.
Even using it on the tank is slightly worse than not using it -- both sides get tp faster which makes tp moves come more often, annoying the BLM and slightly increasing the danger that one will land while shadows are stripped and the tank didn't get them back up due to recasts/paralyze/silence/whatever.
It would be great for content like classic Dynamis, Limbus, Einherjar, or Nyzul where you have a lot of mobs to kill in limited time, probably have some CC'd, and you want to deal as much damage to them as possible quickly without worrying about how much TP you're giving them. But that kind of content doesn't exist anymore, or only exists in its level 75 form which will be even more trivialized by level 95 players than it was by level 90s. Current content is all about the endurance fights on single targets and TP starving the mob (not to mention reducing the number of players in AOE range) is a crucial part of the strategy for nearly everything.
Unless and until SE brings back many vs. many content, Temper will have little use and less desirability.
That's why SE gave us Addle, which actually works on spellcasting HNMs (because unlike other enfeebles, its effect when it lands is not powerful enough to drastically reduce the difficulty of an 18-on-1 fight). Why they then turned around and gave it to WHM, I have no idea -- it's not like WHM have trouble getting into parties. But maybe WHMs will decide that they're too busy to keep up Addle and suggest that the party invite a RDM to do it. (Or maybe they'll actually have resist problems with it -- after all, they don't have +40 skill from their AF, AF2 and AF3+1 alone; for that matter, they don't even have an A+ rating in enfeebling.)Still waiting for that enfeebling magic update too - it'd be nice if every NM under the sun wasn't either super resistant or outright immune the spells that would help most for that fight - like Silence, Break, Gravity etc. God forbid a RDM may actually be able to perform it's intended function.
I'm less bothered by BRD getting a similar spell, since, for one thing, they might stack. Songs generally stack with non-songs with similar effects. Even if they don't, BRD is rare enough to not be a major threat to another job's invite rates.