I don't believe that poor coverage is the reason your budy's SPOT didn't work in baja.
I might agree with the possibility of "user error," except there were points in northern Baja so the individual knew how to use the device. Plus, I'm not the first person to make the observation that Baja is not covered well by SPOT.
I have not seen any recent evidence to suggest otherwise. Personally, if I have 300 bucks to waste on a SPOT before my next trip I will settle the debate once and for all. Having the ability to notify family and friends that I'm OK, and where I am, would be reassuring to both them and myself.
