Wow, I thought I was incredibly picky about centering. That is imperfect, but only just. To be honest you can't really expect better than that on a mass-produced light. It is relatively common with some brands to see LEDs so off-centre that one of the silver corners (or even both) are almost completely hidden under a reflector with an opening that size. At least 4sevens uses centering mechanisms, so you never see any more than a fraction off-centre.
A spec of dust or something of that size on the lense is also very common I'm afraid, and it wouldn't be too uncommon to find something 3 or 4 times that size on an LED dome. It certainly won't affect the output to any noticable degree. It seems to be near the top of the emission angle on the LED and so probably wouldn't be blocking light to the reflector but light that would go directly to the spill-beam. Try shining it on a white wall and see if you can see a dark spot anywhere in the spill-beam, I would guess it is too small to have any noticable effect though.
All in all, that sample doesn't look too bad. You could have done slightly better, but it could've been quite a lot worse, especially from some other well-known brands.