I haven't used the Hagen one, but I've been using the Red Sea kit for over a month now. Here's my opinion on it so far:
Pluses: Nice sturdy bottle that can be hung on the back of the tank (easy to keep out of sight). Bottle cap has a good O-ring seal and a small output to attach the tubing.
Minus: Bottle only holds 1L of water (so less than the volume usually recommended for 2L soda bottle DIY mixture).
2. Diffuser pump
Pluses: Small & very quiet. Dispenses micro bubbles when plugged in, but the gas can still escape out of the pump output when off (i.e. the pressure doesn't build up, it will just release a big bubble once every 10sec or so that floats up to the surface and bursts). The pump also helps spread the CO2 bubbles around the tank.
Minuses: Pump can take a while (up to 2 hours) to get going when plugged into a timer and the timer goes on. Also makes a horrible noise while it did this. Although it could be because I plugged it on the same timer as the lights. Might be ok when using its own timer. Anyways, I now just let it go 24/7 as the CO2 output from the yeast tends to be lower at nights anyways (I didn't see a measurable difference in pH at nighttime when it's off vs on).
Overall, it's a pretty sturdy system. Not bad since you get a pump which you can use for something else and a nice bottle (no messing with leaking caps, etc.). So far the maximum CO2 output I can get out of it (with 3 different sugar/yeast mixtures) is 15-20ppm in my 23g for about 2 weeks.