I used to have 2 DIY CO2 bottle for my 10 g, but it was almost impossible to overdose CO2 especially with DIY. I wouldn't worry about overdosing it as long as you follow the known recipe in the forum. I inserted my co2 tubing into a small powerhead under a timer, so it only diffused co2 mist during the day and stopped at night. (Once the powerhead stops, co2 bubbles stay inside powerhead or a big blob of bubble just goes straight up to the surface.) Eventually I didn't like the bulk of powerhead and it sprayed out too much mist so I took it out and switched to two glass diffusers for each bottle. I wasn't able to stop co2 at night, but my fish never showed any signs of gasping or stress and never had overdose issues.
But, after 6 months dealing with yeast bottles and sludge build-ups and fluctuation in co2 level, I decided to get a pressurized system and now I am much happier with the result. Everything is now so much easier and cleaner. After only a month, all of my algae is gone and I didn't have to make yeast bottle every 2 weeks, no need to clean diffusers every week, and I can precisely control co2 level. I also have a space issue, so I got a small 2.5 lbs tank. I think some people also go with ADA system or paintball system for a small space.