So today I have a comparison of Nina Ultra Pro in Sailor, vs RBL (Rescue Beauty Lounge) Dead Calm. They are near identical in colour. opaqueness and application. Their biggest difference is in their price with the RBL at $18 and Nina Ultra Pro at around $4 depending on if you have a Sally card or not.
Both are a beautiful deep dark navy blue creme. Love at first sight.
These are both lovely polishes and I would be happy with either one. Another very similar polish is Essence Just Rock it! which is an even better deal at 99 cents, but it is a smaller bottle.
I will be posting a swatch of that soon and when I do, I will link it here so you can compare.
Thanks for looking!