As far as I know it's all antidepressants that are avoided with bipolar. That's in the "ideal" world where a mood stabilizer on it's own does the trick or when you're not depressed. They're not always effective at helping bipolar depression nor preventing it and can make things worse, that includes SNRIs and others. Of course, psychiatry is all about trial and error so, when the first approach doesn't work, another one is attempted and the "rules" are broken on an case by case basis.

I haven't read anything about SNRIs working better for bipolar depression but, as a second choice after a trial or two on an SSRI makes sense.

In case you're curious, Wellbutrin isn't an SNRI or SSRI, it's in its own class. It affects norepinephrine and dopamine. That's why it decreases appetite and is often prescribed with an SSRI and helps with quitting smoking and was marketted as Zyban. Same drug, different name to increase sales. It's also a third or fourth line drug for ADHD because of the stimulant effects.

SNRIs approved for depression are Cymbalta, Effexor and Pristiq. Pristiq is actually Effexor but, a more potent version that was put on the market because the patent on Effexor ran out, it's just a drug company scheme to keep profits. A lot like Symbyax (which is just Zyprexa and Prozac) released after both drugs were off patent.

Enough of the tangent!