How are these for cooling?

So I am on my first batch which needs another 9 more days before I even consider bottling and I am already thinking of batch #2. I want to build a fermentation chamber inside a cooler and found these Rubbermaid Blue Ice® Weekender

As per my calculations I can put 4 pieces on each corner of the cooler for a total of 16 for a grand total of $35.04 + shipping. I think it would be a better alternative to using ice in bottles since this should keep colder for longer period of ice and hopefully keep the temperature cold enough without frequent "ice" changes.

What do you guys think?

I haven't used this particular blue-ice pack, but I've found that they last just as long as frozen water bottles.