I don't see any option to turn Legacy on, or any setting for airdrop at all.
Have a MBP 5.1 (late 2008) as beta machine with OS 10.10.1 (the beta seed of the update, didnt work before neither) and a 10.1 (mid 2012) with 10.9.5.
Transfer goes neither way, both appear, but when drag and drop, both say "waiting" and then "failed".
My conclusion:
Apple forces, like Microsoft, over incompatibility to buy new machines. Difference between windows and mac was that mac didn't force you to buy the newest product. I was proud of that, as a mac user for 18 years, and made me identify with the brand.
Because of two reasons:
a) IN THIRD WORLD we use have to use old stuff, hardware and software have still prices of first world, so what is cheap there is f... unavailable here!!!! IT ISN'T THE SAME ON THE WHOLE WORLD. Now Apple got also into the des-democratization of access to technology, magnifying the gap, what a pity (is somebody of Microsoft infiltrated to make it loose their public?). On the long term, I will have to use only Linux (right now the beta-machine has a parallel Ubuntu)
b) Macs were working machines. Now they are chatting machines. I can't afford a tablet, but if I would like iOs-funcionality, I would buy one instead of a MBP. And if, an Android, it is cheaper and I don't need as much quality when it isn't about work....
Sorry, off-topic.