need for dial altimeter?

I am in the process of designing the instrument panel/layout for my
HP-24. Still a ways to go before I will need it, but it is raining out
and my CAD program is running and so is my
imagination..........so.............I was reading about the new Tasman
Data Module on Paul R's website and see that it provides pressure
altitude.

I will be using a GPS to run my PDA, that gives GPS altitude, if I use
the Tasman vario and data-module package, would I really need a dial
altimeter?

Thanks,
Brad