I don't think Blyxa japonica will grow well, if at all, in a low-light, low-tech aquarium. But, the "star grass" might do ok. I only grew both of them in a high light, with CO2 tank. The star grass was a weedy pest, suggesting it could make it ok with less light, while the Blyxa grew very well, but seemed to need the high light and CO2 to do it.
Blyxa was a no-go in all of my no-tech, low light planted vases, but I've got one remnant going strong in my 37g low-tech/medium light setup. Might be coincidence on the timing, but it was melting with no growth in the tank while in the mixed fluorite/gravel section, but rebounded and started putting out healthy green leaves and significant root growth when I moved it over to a newly added sand section (tank has sections of sand on the far right/left with fluorite/gravel along the back and filling the middle section).
Stargrass grows well in my no-tech planted vases in the higher ranges of low-light --but shows a very rangy growth pattern with thin leaves and long stem sections between leaf nodes. A very different plant than under high light/c02 conditions. Still useful--but very different.
Laural I had it in a low light tank for about a week while I was at work and it was almost completely melted when I got back home. Then moved it to the 10gl and its been there alittle over 4 months now with no Co2 and im dosing iron and micros every other week.
I have both and they do well. The blyxa is in a small Spec. It is lush and beautiful I only do root tabs in there. The Spec is small so there are only 3 plants in it.
Stargrass has done extremely well for me in my 40B. I keep it cut to about 5 inches and it is a beautiful hedge. The 40B is dirted. I think the worst part for me is how easy the stems break when you mess with them.
I say they are worth a try.