I don’t entirely agree.
PDAs are a robust product and in my experience are every bit as reliable as traditional GPSs. I have used an iPAQ for sometime now very often combined with a Garmin 195. Neither has yet failed which is more than I can say of some of the panel mounted avionics.
That said, PDAs have relatively poor battery life and it is essential to run the PDA with the backlight on making matters worse. The same is true of the GPS be it a Bluetooth or a wired modelled. In short both units should be wired into the ships power if you want to be certain. Whilst I haven’t found the PDA has ever “frozen” the soft reset is easy to use and there is no reason for not doing so even in flight.
PDAs have several advantages. The screens are very clear, the unit exceptionally light so it can be yoked mounted with ease and often the user interface is very good. For example on the software I use a tap on the VOR, airport, or user reference point enables you to route direct as a new flight plan. I also like the ability to display in the same way the extended centre lines of runways to effectively give you a 2D ILS.
I have also been use PocketFMS for a while. The maps are excellent. IMO the user interface could be a little better but the software is improving all the time. I particularly like AnyWhere, however unfortunately the maps are somewhat out of date but the user interface excellent. It is a shame the best of both products is not available.
If you do decide to go this route it is also important to be aware that the software can either be stored on a flash card or within the PDAs built in memory. Unfortunately the built in memory on earlier PDAs is dependant on the PDAs battery not being exhausted and of course you can bet if you leave your PDA on the aircraft they will run down as they slowly discharge. Go for a new model or better still store the software on a flash card.