Over a 24-inch 20g I would not use dual T5 lighting; that is going to be way too much with even NO (normal output, which is basically equal to the T8 tubes) and with HO (high output) you would have algae soup.
Your 10g is beautiful, by the way. You log data says you have a 15w T8 tube and a LED. You don't want to go beyond this on the 20g.
I have not personally tried the Marineland DoubleBright LED, but Jeff has had good results and I have heard that it should be a good light. So I would consider that. If money is an issue, another option is a basic incandescent fixture taking two screw-in bulbs, and using the 10w "Daylight" CFL bulbs with 6500K. I use GE bulbs over my 10g and 20g (see photo below) and the plant growth is good and algae is non-existant (compared to my larger tanks with T8 fluorescent tubes). This tank is my QT for new fish now, and I thinned out most of these plants, but the photo is illustrative of what is possible under two 10w CFL Daylight bulbs.
Byron.