It works OK for me on Mac, but all touchID drops to about 50/50 for me in Winter, under the (otherwise) best circumstances. Dry air, I guess.

On iPhone, specifically, it was awful for me. I was too likely to have wet hands (raining, just got out of shower, whatever—even dried, the higher moisture in my skin meant it didn't work) or gloves on or some other problem that made it fail. Trying to hold it the right way, one-handed, to get a finger in the right position (waaaaay down near the bottom) was also a high-risk maneuver for a drop, and was not a way I'd otherwise have tried to hold the device.