Number of antennas only matters when the unit is in search mode (.i.e., when looking for somebody else). For keeping him safe it makes no difference .
There should be no selfish thoughts like this when it comes to beacons. If you cheap out and a mate dies you always have that hundred dollars or so on your conscience. Likewise you would hope your mate buys a 3 antenae beacon so he can help find you quickly in a burial.