No one should be reliant on it. But they are good to have. I would much rather have a medic have the tools to look up a med dosage they don't know, then risk them guessing and give the wrong dose of something!
I use mine mainly for looking up a Pt's med, that I may not know what it is used for. It is the same as carrying a pocket guide. Any medic that does not have a backup, is not prepared. No one can know every drug on the market, so it is smart to have something you can use to look it up.
If a medic can't do simple conversions, then they should not have a license!
It's my personal belief from what I've seen that any backup should be in the form of books. However, my main point is that most medics now are using electronic devices as their PRIMARY AND BACKUP method, and it absolutely cripples them if something happens to that device. And things happen to those types of devices. Again, I've seen medics absolutely paralyzed without their electronic devices, and that's scary.
What they did for us in school was prevent us any use of ANY electronic helper, from calculators to PDAs until after we had proven our knowledge and skill in doing it in our head and using logic/reasoning. Sadly, I don't see that's the case everywhere. So I believe PDAs are fine if used as a secondary source, and should NEVER be used until after you're proficient at figuring things out the old fashioned way.