I can use it to see where in the queue my courier contract is and so get an idea of how long it will take before it is accepted.
All it requires is for each alt that uses it to create an API Key (access mask 0) and then register with the site.
Given i use my corp to set up the courier contracts then i don't need to use this site ingame - i can readily use the ingame contract tab to check.
However, out of game it is useful - no more do i need to log in to Eve to check the status of my courier contracts. I can use my ipad to check the status and then log in to post the items once Push Industries has delivered them.
To date, i have created 601 contracts with Push Industries, total fees paid of 13.8bn ISK, total collateral Push Industries have put up is 714.1bn ISK, total volume hauled 2.7m m3 and total warps 9536.
I suspect there is more that can be done with this - for example, an email could be sent once a contract is completed.
But, so far, i like it.