Try the online demo and punch in something like a 60' dive for 60 minutes. Oops, overlimit, sorry bub, we aren't going to give you any useful info. OK, now what?
And if its so easy, why to you have to convert to EAD for nitrox dives? Where's the altitude adjustment? PADI tables tried to be idiot proof but they failed. As long as you understand how tables work, any other tables are more straight forward and less cluttered.
Anyway, whether you have a dive computer or not, IMO you should either take your tables with you or have at least a subset of your tables for your current dive plan plus some contingency numbers (a little deeper and a little longer than your dive plan). Some people here say that relying on a dive computer is dangerous (and I don't necessarily disagree with them based on how I've seen them used). But relying on some non-depth-resistant mini-calculator back on the boat is absolute lunacy. My two cents....