I'm a 375 blacksmith with the boots of the protector recipe (I think most smiths in my guild have it now) and I would say that is is definitely not worth dropping a profession and levelling blacksmithing for this recipe. They're a threat-oriented sidegrade on the battlescar boots from Karazhan.
I wear them in my threat set, not in my regular tanking set. You don't need to be a blacksmith to wear the belt of the guardian, so that's not relevent to your choice.
If your guild is not in SSC and you are thinking of buying this recipe off the AH then you should be fine with elusion/battlescar from Kz. If you are in SSC then you should be working towards BT where the first boss drops boots that are far superior.
There are tanking jobs in SSC/TK where you would want a good threat set (A'lar adds, Leo, VR etc) but if you have to level BS from scratch to get these boots then my advice to you is find another source of spell damage.
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