I only ever played with a Freemage once. Yes, it was nice for secret doors, but not really worth it, IMHO. I found that you could acquire that special "pet" that would sniff out secret doors at about level 15. (A really gung-ho player could probably defeat the baddies guarding "the pet" a lot sooner, but I was taking it easy.) Up to that point, I depended on scrolls, which were readily available. They varied in cost depending on how many turns they were good for [one turn = one step or other action.] If you were really short of cash (not too often, in this game,) you could save/use scroll/examine walls/reload/repeat, but that's really cheating, in my book.
Incidentally, that "pet" can actually be a member of your party. Your party of four has two extra slots for additional members. At one point, however, it is necessary to have both slots taken by others, in order to finish the game. If the "pet" is released, he goes back to where you found him, and will rejoin your party whenever you ask.