Bearing Buddy is completely different from Dexter's EZLube and AL-KO's AG Hub (aka UltraLube, I think) systems.
With BBs, grease is pumped into the axle
from a zerk in the dust cover, goes thru the outer bearing, fills the air in the hub and expands a spring in the cover -- In theory, when the warm hub is dunked in cold water at a launch ramp, instead of water being sucked in past the seal, the spring moves -- Problems that seem to arise is that if the grease has stiffened, the spring may not move -- Also, if the hub gets hot, the spring is putting tension on the hot grease and the only outlet is the seal -- Also, there is no way for new grease to get to the inner bearing unless the seal is leaking a lot of grease.
With the other two systems (now provided on many axles), a rubber cap in the dust cover is removed, exposing a zerk set in the center of the spindle -- Grease pumped in (slowly, by hand pump, not compressed air gun, with the wheel jacked up and turning slowly, according to Dexter) goes down a hole drilled in the center of the spindle and emerges between the seal and inner bearing -- Taking the course of least resistance, the new grease goes thru the inner bearing, then the hub, then thru the outer bearing to emerge by the zerk -- If the grease expands, the rubber cap lets the grease escape
on the outside of the hub, not thru the seal and onto the brakes
a nifty animation showing AL-KO's system.
According to the moderator on a pop-up group, Dexter and AL-KO did a lot of testing to ensure that a hub full of grease didn't cause problems compared to bearings greased the conventional way with a hub full of air.