For wireless cracking, dual band is pretty much useless. I do have the AWUS051NH and it does work well on 2.4GHz, but there is very very poor injection support for the 5GHz band (not really sure why). Regardless, if you aren't going to be using them to connect to a network, I would go with an AWUS036H. Uses the RTL8187L chip which is very well supported under Linux for injection. If you really want a dual band card, I don't have experience with the AWUS052NH so I can't recommend it, but the 051NH does work on 2.4GHz, but there is no 5GHz injection support.
