Both are fine kits.
For the ISW kit, it is one of their better offerings. It is offered as whole hull only, although you could special offer it 'poured short' to make a waterline version. MSRP price at the ISW site is $165.00 (USD), which includes the ISW customer satisfsaction guarantee.
http://www.commanderseries.com/pages/Ainsworth-Judy.html
The WEM kit is also very nice. While it is listed in their catalog, it may be OOP. Check with John Snyder @ WEM regarding availability. The WEM Knox is a two-piece hull. While it does give options there are also some attendant potential warping & fit problems in assembling the lower hull. The MSRP at the WEM site is L112.30 (GBP) - this converts to $213.60 (USD) at todays exchange rate.
http://www.whiteensignmodels.com/brochure/1_350_knox1.htm
Your selection of either would be a good choice