Back bottle group buy

I’m going to make an order for a couple of these back bottles: https://backbottle.com

Trying it out for long rides on my single speed that has no bottle cage mounts.

It works out at US$51 for 4 bottles delivered (on a buy 4 for the price of 3 deal) = AU$67 = $16.75 each.

I only want two. Anyone else keen on the other two?