Can't help you with the Narex, but I just recently picked up the Grammercy Tools 6 1/2" and 9 1/4" rasps, and am very pleased with them so far (they're two weeks old, so obviously I can't speak for their longevity). I will definitely get their 12" rough cutting rasp when the need arises for a larger model.
When you say @DzordanoBruno that the Narex have to be sharpened, do you mean some sort of chemical treatment? I can't imagine one can refile the individual teeth.
Are the Narex rasps hand stitched, btw? EDIT2: Just checked product info and saw that they are uniformly/machine stitched
EDIT: here's some info on the Gramercy Rasps
The sharpening of rasps and files, is something that has been around for ages, and which is sometimes actually part of the manufacturing process, but which doesn't seem to be commonly mentioned much now in most technical literature.
One method involves dipping the files or rasps in acid. I've seem mentions if muriatic and phosphoric acid, as well as possibly even using white vinegar. This mostly seems to be mentioned in regard to old worn files, but it is common to clean steel that has gone through a hardening and quenching process with acid, so it may actually be part of regular file and rasp manufacturing as well.
The supposedly better method for sharpening files involved blasting the file surface with a combination of abrasive and compressed steam. The angle at which the surface is blasted may vary depending in the type of file or rasp, as well as possibly the type and size if abrasive. The technique isn't new. I'm not sure how old it is but I think it goes back to at least the late 1800s when some files were still being hand cut. I'm not sure how many file manufacturers if any still use it ad part of their manufacturing process, but I ran across an old article explaing the manufacture of Vixen files, and it was specifically mentioned as a separate step used in the manufacture of the files.
There is a USA company called Boggs Tool and File Sharpening Co. that specializes in sharpening files, rasps, burrs, and other tools using this technique. I'm not sure if there are other companies that do it as well.http://www.boggstool.com/page74.html
WKFineTools.com has an old article on the process in the website.http://otools1.wkfinetools.com/filesT/y_UsingFiles/1879-SandBlastSharp-AmMachinist/1879-SandBlastSharp-AmMachinist-01.asp
There are also float files which are not always fully hardened, or at least tempered softer than regular metal files, and which a meant to be sharpened with other metal files, or abrasive files such as India or Arkansas files. This is a Lie Nielsen video on sharpening floats.
SawmillCreek had a thread mentioning acid sharpening, and there's a video on Youtube.http://www.sawmillcreek.org/showthread.php?166743-Can-I-sharpen-a-file