There are two standards depending on the country. In the UK 1 (Imperial fluid) ounce=28.413mL, but in the US it's 29.573mL. Even though you may be using US currency to purchase perfume, the perfume may be manufactured and priced according to the standard in a different country.
1mL=0.0338oz (US); 1mL=0.0352oz (UK). So 2mL=0.0676oz (US) which is more than 0.05oz.
The first ad is selling 1mL for $3.68, which is about $108.86 per oz (US).
The second ad is selling one 0.05oz bottle for $1.6725, which is $33.45 per oz (US) (compared with $108.86 in the first ad). 0.05oz (US)=1.47865mL. Therefore 1mL costs 1.6725/1.47865=$1.125. So the second deal is much better value for money. The perfume in the second ad is 69.3% cheaper per bottle than the first.
It should be borne in mind that multi-buy sales are usually reduced compared to single item sales, so buying 4 bottles of perfume as a multi-buy offer is cheaper than buying 4 separate bottles. Also, the bottle has to be manufactured at a cost which can vary depending on the design of the bottle.