I am not certain that Hyponidd is the "herbal equivalent" of Metformin - it is just reported to be as effective as metformin. I believe that Metformin's primary effect is to alter or slow the liver's release of glycogen (similar to gulcose) and that it also may have some insulin sensitizing effects at the cellular level that are not well understood.
Hyponidd is a blend of over a dozen herbs that seem to have a variety of effects that might affect glucose/insulin metabolism (see thread
Hyponidd Ingredients Chart - Very Informative!) - although perhaps not everything about how Hyponidd might work is completely well understood either.
I have heard that there is a herb called something like "goat rue" that might have some similarities to metformin in the way that it works. I do not know of any cysters using it.
I believe that Actos and similar drugs do having an insulin sensitizing effect at the cellular level and that that is the primary beneficial effect. They might work by having some effect on peroxisome proliferator-activated receptors (PPARs). It might also work by activating Protein Kinase C-zeta. (PKC-Z). This article:
http://www.medicalnewstoday.com/articles/44409.php suggest that the undersirable effects of another drug in the same class as Actos, Avandia, might be due to the activation of Protein Kinase C-beta.
Exercise might be though of as something of an 'equivalent' to Actos - without the water retention/weight gain/edema. Exercise can a significant insulin sensitizing effect (perhaps greater than insulin-sensitizing drugs) and I believe it also effects PPARs and PKC-Z.
There may be herbs that affect PPARs or PKC-Z in a beneficial way - but I don't know what they are.
One herb that is purported to have insulin sensitizing effects - that I think is interesting is Banaba Leaf Exract. I don't know enough about either Actos or Banaba to say if there are any similarities in the way they work or how they might compare in effectiveness - I also don't know about using Banaba is you are trying to conceive. (note the 2nd to the last letter in the word is a 'b' not an 'n'.)