Seidio batteries have been shown to not be as advertised. I would be careful.
I have used Seidio extended batteries on my last 3 devices, all being Blackberries. All have worked very well and as described. They have all arrived and looked as advertised. All three occasions, I have not had any complaints.
That being said, I have no intentions on getting Seidio's 3800 on my Gnex. It dramatically diminishes the visual appeal of the Nexus. I will be content with my OEM 2100 extended battery, and preserve the clean lines of the phone.