I don't have the charging dock so can't comment on it.
These two batteries look the same to me except the $5.80 one seems to have a yelloew sticker with a wholesales vendor's name on it. The $9.50 one shows an extra "Built-in safety and protective circuitries" feature in the description.
I have a different pack, SKU 57931, from them. It comes with a bettery but I am not sure if it is a $5.80 or $9.50 one since there is no serial # on the battery. After initial full charge, Streak uses about 25% per day. I have very mininum phone usage (few quick calls/texting/WiFi. I don't have 3G service).
Even it is a $5.80 one, it seems to be working fine for me.
BTW, it took a while to finally receive the shipment in US. (about 4 weeks after placing the order).