About the only difference b/w Vent and CD is Vent has an auto-round feature for skeet, where it automatically cycles to the next target, in other words, you start on station one, it throws a high, then a low, then a pair, and so on, with no user intervention, although you need to override it to shoot a target over (ie your option shot).
The current gen clay delay has auto high-low rearm, you activate the high, it rearms on report for the low, then you'd have to rearm for doubles. Previously (the generation I have) you have to arm the trap for each shot, not a big deal if you load one shell but could be a pain if you load 2.
The CD has auto-rearm for trap, so it's completely a wash for trap.
The only real advantage of the Vent is for skeet, and even then only a minor advantage if you load 2 shells, if you load one shell for singles, put the transmitter on your shell pouch and hit the button when you grab a fresh shell.
The CD is also 1/2 the price of the Vent!