Legitimacy is not defined by whether "unlocking is legal" or not. Legitimacy is defined by the reliability and whether or not they deliver at all. There are plenty of websites that routes you to a middle man, takes your money, and pretends nothing's happened. Or, they over charge for the service. And because 99% of these "other unlocking sites" you're referring to sells jailbreaking services as well, that just drags down their reliability because they're scamming the unknowing by charging them for 5 minutes of their time of what they can do at home for free.