How many gallons is your tank? I started with a 10 gallon that had HC, ricca, moss, and various stem plants. At first I used the fizz factory from Petco and I didn't really see too much difference. The CO2 was was not consistent enough where I saw growth or pearling.
On the other hand, I later converted to DIY with a diffuser from ebay. I saw much more growth and great pearling from my ricca. It's rather inexpensive to run, but can start to be bothersome after awhile. The Co2 would get weaker by the 2nd/3rd week, so you'd have to run 2 bottle setups with one made 2 weeks prior. Well, this was too much of a big headache, so i converted to pressurized.
I'm sure the Hagen system is a better option than the fizz factory. It looks to have a better consistency of CO2. As Brad has stated, a good first option to start out with, but I'd rather save the money and start with pressurized. After going all these other systems, I could have saved myself the trouble and started with pressurized from the beginning.