Most of the Windows updates are not critical (many are for networks) and missing out on a few will not leave you open to teh Hakerz. You can do a manual update once a week if you want...it takes little time. Just use a good, free AV such as AVG/Avast and any old antispy programme (free of course...Superantispyware or Spybot) and you will be more than safe.
There is a huge amount of hype and paranoia about the 'evils' on the Internet and the legions of nasty people trying to steal your info....much of this is advertising speak. Use some common sense and you will be protected against all or imagined 'attacks' and check occasionally with MS..it is sometimes better to leave updates until many have tried them, so that you avoid any problems *cough* SP3 *cough*
The efficacy of Onspeed is, ate best, dubious and a quick search on this site will show the debates.