Yeh, you know I think you right. for example deore cranks are some alloy of some sort, most crank tools are steel, I guess it just depends on how tight the cranks are in the first place. If there not tight they'll come off fine, but if the BB axel has rusted and expanded you might have a chance of literally tearing the threads out of the crank.... That said, I had one of them park tool ones with the lever attached to it so no use for a spanner, it was seriously well made, very smooth movement on the threads etc.