Anyone tried the new fibre block on sale?

I saw the Feedmark ones via email yesterday... but the Halleys ones look better (and cheaper :) ). Was thinking of getting some for putting in the field - the problem I have is that my field is quite exposed and windy and they hay just gets blown away - was thinking these won't blow away!
 
they look like a great idea, quick question tho it says they can be put in a haynet but as theyre obviously brick shaped can the ned get to them thru the holes ok? may be a silly thing to ask but hay pokes out and this wouldnt?
 
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