Once you bottle with them, they will get wet, which starts the O2 "collecting" (I don't think they actually absorb O2 as much as modify it in some way. I mean, they can't really just "hold on" to O2...).
The process takes a while, so you are not going to ruin them by spritzing with sanitizer just before capping.
I got some when my LHBS didn't have the regular caps and they seem to be ok. I have not tried them long term enough to know if they are better for preventing oxidation than regular caps, but the price difference is not enough to make me want to use the regular caps anyway.
The best thing you can do to prevent oxidation is to handle your beer properly during the fermentation and bottling stage. Minimize the exposure to O2 by not splashing, and blanket your containers with CO2 if possible. And "cap on foam" which pushes the O2 out of the bottle just before the cap is pressed on.