Jointer blade honers, do they work?

[cgallery]

Rockler and others advertise honers that can be used for jointer knives without removing the knives from the machine:

http://www.rockler.com/product.cfm?Offerings_ID=2419

No reviews at the Rockler site or Amazon.com, for that matter. So I wonder how well these work and if I can prolong use between sharpenings?

Thanks,
Phil

[cgallery]

I guess my real question is, does honing just tune-up already sharp knives or does it further sharpen blades or what is the purpose of this gizmo? Any comments?

How do I know if my jointer knives are sharp enough if I purchased the unit used and don't know how it worked when new?

Thanks,
Phil

[Bruce Cohen]

Well I hate to admit it, but I bought something like the one from Rockler, and in a few words, IT SUCKS!!

Bruce

[LCHIEN]

Well I hate to admit it, but I bought something like the one from Rockler, and in a few words, IT SUCKS!!

Bruce

I guess the ones from HF must be really bad, then...
still unopened in the package...