Probably only the retail margin Danny! ( If you mean the merchants are cheaper! )
Having said that, there is a wide difference between the bendability of the different makes on sale. This is not very important with 15 mm but with 22 m it is!
I often find that the merchants are MORE expensive than B&Q etc. One fellow at a merchant explains this as "its difficult to compete with B&Q ".
Compare the prices very carefully before coming to any conclusion on an exact like for like basis.
I can, it's harder! As you say, Frog 22mm on a cold day is something to let the apprentice bend.
For a long time the cheapest was Wickes, maybe not now.
"Half hard" is an indication of "temper", bothe are supposed to mean hardness and strength , roughly. Pretty wide spec though, and it depends on the purity of the copper in the first place. It only takes 0.01% Ford Cortina...
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