Upon further reflection:
On the one hand, Lee Valley sells awesome tools. The best splitting axe I have ever used came from Lee Valley, I would immediately recommend anyone to buy Lee Valley tools.
On the other, at 12.50 a knife, retail price, corners are being cut somewhere, once you get materials, labour, transport, packaging, etc. paid for, how is the store making any kind of decent profit off the knives?
I have no clue what '420 stainless steel' is, from a quick google I ran across this:
IIRC (And I could be wrong, this is all theorycraft), Japanese knives traditionally hover somewhere in the 60-63 range. Would this not require the Lee Valley knives to use a more european bevel angle in order to keep a decent edge?
I notice you asked about 'usefulness around the kitchen', and this is where I could see myself hating the knives.
The paring knife is 5 inches. I hate paring knives with 5 inch blades. I have a beautiful MAC paring knife with a 5 inch blade, I keep it around so that I have a knife to give the dishwasher if they ask to borrow one for prep. I find 5 inch paring knives too long to do any precise work, and too short with poor geometry for any chopping, dicing, slicing, etc.
The santoku has a 6 1/2 inch blade. Now, I really don't like santoku's in general, I always find myself wishing I had just used my chef's knife. That's just me though, I know tons of people who swear by them.
The slicer has a 8 inch blade, I personally prefer a much longer slicer. Again, this is my personal preference.
In conclusion - Lee Valley makes good stuff, but I find these a little iffy. I would recommend sinking more money on 1 nice chef's knife than these 3.