Solo climbing devices

I am thinking about purchasing a rope solo belay device such as the Slient Partner or Soloist (see: http://www.wrenindustries.com/). I perfer a device that will lock no matter what direction I fall, such as the Slient Partner, but it is expensive, and looks cumbersome with all the backup knots. How steep of a climb have you used the Soloist without any problems? Has anyone had any experience using this that can share some light on the subject? Thanks, Terry