i posted the same question on the ukc board before i got the 40. i could'nt tell with that post if they were better or worse. 6 of one thing saying junk and half a dozen others saying they were good.
the video i watched on youtube showed them on a magnet mount antenna at 6.27 miles and losing the signal on the 30 and the 40 at about the same time.
one thing i like on the 40 is it has a plastic cap insted of the metal as a top clamp holding the battery and unit to the collar.. i changed alot of 30's over to the day glo collars and man the 30's really corrode bad. them lil screws will weld themselves in and you will not get them out. you will strip the screw head. then your kinda screwed as far as changing the collar stap,the battery or the antenna.
first thing i did or do is change them lil screws to allen head screws.garmin puts locktite on them,,i put never sieze on them.
same goes for the clamp for the gps on the 30.. i changed my 40 over to a green dayglo that was made for the 30 and with the unused wire sleeve and antenna loops it gave me something to run my antenna on the 40 through.the antenna is kinda just hanging out there flopping around in the stock form when you buy them. they zip tie the antenna to the collar.
my dc40 w/tuff skin and dayglo.