Just a quick little review on the OPI Rainbow Connection dupe, which I bought off ebay.
I applied the glitter polish over Sephora Metro Chic and Models Own Purple Mystique. I don't have OPI Rainbow Connection, but from the swatches I have seen online it seems like a pretty good dupe. I used two coats of it to achieve the amount of glitter seen here, but I can imagine it would look amazing with one or two more layers. The polish applies well and dries pretty quickly - I'm really impressed with this, especially for the price I paid for it.
I bought this from this seller for £2.99. I'm guessing the seller has realised how popular this nail polish is as they have upped the price to £6.99 - but I have found one cheaper here if you want to get your little mitts on it.