CO2 is
most definitely worth it under the right circumstances. If you just want plants with your fish then meh, not always worth the capital cost and many plants can grow low tech. However, if you really want your plants to pop and you're growing slightly more demanding species then definitely. I used it on my scape to grow Monte carlo under medium light (12W LED) in my 15 gallon/60 liter tank, this is a year in
Now the tank was flooded since April with a 2kg bottle, it cost me +- 3 GBP to fill and it's still running strong. Running cost is low, capital is a much larger issue. My setup (2kg capacity cylinder, dual stage reg and solenoid) was 90 GBP/ $110 second hand. After that it's a breeze. I don't have any specific brands I see used, just make sure to get a quality regulator and solenoid. Extra money worth it for durability and safety. Hope this helps!