For what it's worth......
I have a 55 gallon community tank that has "evolved" into a pretty heavily planted tank (~3 Watts per gallon). I have never bothered to go to a pressurized CO2 system (2 x 2L bottles) on this one as I get strong growth and healthy plants using DIY CO2 supplemented with ~5 ml of Flourish Excel every third day.
It's difficult to say how much impact the Flourish has vis-a-vis the DIY system, but conventional wisdom says that the DIY system shouldn't have enough "horsepower" on its own. I grow a wide range of pretty common plants including Crypt.s, swords, Anubias, Bacopa, etc, etc, etc. I see regular pearling on most of them and they are certainly healthy. I ripped out both wisteria and hornwort because they became uncontrollable.
I have never seen any adverse effects on the fish or any change in behaviour when I dose the Excel.
Hope this may be helpful,