I was looking at both of these for installation on an SAR-1.  

I believe each of them are designed for both eyes open targeting.  I don't hink I would use the chevron or open cross reticles on the Kobra but it is about $50 cheaper.

Can anyone advise the advantages/disadvantages of both?

Thanks

Kobra obscures less of your view. The dot/chevron combo makes a great parallax adjuster under 100 yds. I own 2.

Besides being less expensive my Kobras use rechargeable 'AA' batteries so I never have a battery problem. The Kobra has no parallax whereas the PK-A does.
Tomac

Looks like different use of parallax here. The dot does not really move off of the target if you move your eyes behind the Kobra. But the sight is several inches above the bbl, and the bullet is rising up to meet that red dot impact point if you sight it at 100 yds. Using the difference between the impact points for the chevron and dot, you can readily fine tune your aim at varied closer distances.