USB to RS232 (NI adaptor or not)

Hi:

I have to use a USB-RS232 adapter to link my notebook to a device for the controlling.
The controlling will be done through LabView with the VISA  library.

However, I found the price for USB-RS232 adapter varies a lot.
NI has one (http://sine.ni.com/nips/cds/view/p/lang/en/nid/12844), over 100 pounds, whilte there are many other USB-RS232 adapter just cost 10-30 pounds from other places.

What I wonder if, what make NI's USB-RS232 adapter this price?
Is there any compatibility issue (only NI's adapter is compatibile to LabView?) or other driving issue I should be aware of?

I just want to figure out the difference between NI's adapter between other cheaper adapter before I make the purchase (but I do want to avoid the compatibility issue)

Many thanks
Regards, Jhensi