I've read a few things on the Sedio battery, and from what I can tell, Sedio just scams people.
I read a review awhile ago that showed while it appeared the Sedio had more life according to the battery meter, the actual capability of the cell was worse. The phone would last longer from 100 to ~20%, but then drain much faster from 20% to 0%.
Anyway, over at batteryboss a guy has the correct equipment to actually test the cells. The TP2 battery and EVO battery are exactly the same (100% identical/interchangeable) so it makes for a great comparison.
TP2 OEM standard issue 1500mAh
1414mAh png/
csv 94%TP2
Seidio, light use 2 mos 1750mAh
1383mAh png/
csv 79%
http://www.batteryboss.org/
Thank goodness someone is actually testing these and stopping people from getting ripped off.