agree with Suphew, they are a budget model but work well. Mine is a 1000 model, are I think there is a second hand model at Hollywood or PM Jetskisteve.
I rent my bottle through work, $5.00 per month.
I feed my reactor from a small line that feeds off the main return pump to the display, and use a small tap to control it. Saves on a pump and works good. I have a electric solenoid which turns the CO2 on and off, and it is on a timer that I use to use to control Ca and Alk levels. Now with all the growth going on in my tank I have it running 24/7. It is still good to have as it will shutoff the CO2 if the power fails.