I would pass on these. Although the initial cost is low, you will be going through those mini CO2 bottles rather quickly. Especially on a tank > 20g. From the looks of it, you would have to open, adjust, and close the valve daily.
IMO I would continue to do DIY and save up some funds for a regulator that accepts regular tanks. That way you can use either regular or paintball tanks with the use of an adapter. I am using an AQUATEK Premium Regulator with CoolTouch Solenoid with a 24 oz paintball tank plus adaptor. The regulator was $89 and tank was about $25 on Amazon. You might get a better deal on eBay. Filled up the tank for under $5 at Dicks Sporting Goods and there is a deal where every fifth fill up is free. So far I am on my first tank that was filled in early April. I run about 1 bps. Runs on a separate timer; comes on one hour before lights on and off about 30 min before lights out. Worth looking into.
For more info, go to the stickies section in the FW Planted Tank section of this forum. That plus Google should provide a lot of info you need to know. It's not difficult to use.