Looks ok to me, just not a very nice example with the crack and a weak portrait doesn't help. It's scarce, but not rare.
 
	Just because they are round does not mean they are iffy, in fact all the indicators point to some coins of this period being cut out similar to a pastry cutter in the form of a metal tube as you find numerous examples with no wear but a wavy flan, suggesting they have been forced from a tube using a rod.
 
	I'm assuming this is a detector find as an Ethelred Second Hand penny is not the first thing you would find around the house unless dug, in which case the best advice is to pick up a copy of Spink's coins of England or English Hammered Coinage c.600-1272 by J J North (this type being in volume 1). At a few pounds for a previous edition of the first, or 10-15 for the second on anything bar the final edition, it makes identification easy. Much easier than wasting a day trawling the internet for matching images.