I'm using the Fluval Stratum in my 20 gallon right now and I'm really happy with it. I don't have any experience with any other plant specific substrates so I can't compare those but I can tell you my rooting plants like the Stratum 100% better then regular aquarium gravel. I also have the Fluval Shrimp Stratum in my shrimp tank and my glosso absolutely loves it. The shrimp stratum has smaller, lighter granules than the regular Stratum which kinda made planting a pain in the ass.
The only reason I went with the Stratum was it the local availability. I can't stand paying for shipping, especially up here in Canada it's insane
But even if I had other options now I'd probably still buy the Stratum because my plants love it so much.