Ok, I'll admit that I've posed this question on another site but the response has been limited and I'm hoping SH and others can elaborate on the matter.

I see H-fares come and go on the AC web site and know that it is upgradable with a regular SWU and often tends not to be expensive. Can anyone tell me the rationale behind it? What routes is it used on? Is it equivalent to Latitude? What are the restrictions, etc, etc?