I think you'll be glad you ordered the FAS-DPD.

Regarding reliable vs accurate--- OTO is reliable in that it will not bleach out at high chlorine levels, will give you ballpark figures, etc but not accurate meaning it is hard to differentiate between 4 and 6 for example. Very subjective as it depends on user interpretation of the colors.

Here is a chart that may make it easier to understand what I am trying to explain.

http://pool9.net/oto-chart/

EDIT to add - Why would you need both? You don't really. You can use FAS-DPD exclusively but it is more expensive than OTO testing and takes a little longer. OTO is handy for quick daily checks.