I volunteer with a search team. Quite often we are called in to search for folks believed to be dead crime or suicide victims. We use both, but find that a dedicated GPS is much better. Some of the apps for our phones are useful, if they work. Sometimes they don't. A cellphone app saved myself and others from having to backtrack about 5 miles during a search in April. Two weeks ago during another search I found the same app almost useless in another area about 400 miles away.
The accuracy is poor as well. Often we will find an article of clothing, a cell phone, some bones etc. We mark the sight with flagging tape, record the GPS position and call it in for detectives to investigate further. I've seen phones off by 400' on the actual location.
Battery life is roughly the same, although a lot depends on the individual device. But I can always carry spare batteries for the GPS. Not so with most phones.
