Linksys wireless with 'speedbooster'

[puggit]

As in [url]here|http://www.amazon.co.uk/exec/obidos/ASIN/B0002LHXAW/ref=pd_huc_gp_ss_1/202-0595942-2986233?%5Fencoding=UTF8[/url]

What is speedbooster, and is it worth the extra £15 over the standard PCMCIA card?!

I already have a Linksys wireless router, but my current Belkin wireless card has just died :)