The AWUS050NH does not work well with back track, just so you know.
The ND-100 has been great for me, it has a fast lock on and it's accurate. You will need some 3rd party software depending on what you want to use it for.
As for velcrow, I got these half inch circles from the dollar store and they work great, these cards are really light and it does not take much to hold them on.