I have no idea if they help reduce nitrate, all I know is they look just like the clams that SWF are selling as nitrate reducing clams. They are filter feeders and I have not researched what the can do for a tank. Have they hurt the tank, No.
Are they they the silver bullet for nitrate reduction, IMO
I am going to toss some in my fowlr
main tank soon and I will try and monitor the nitrates better to see if adding more makes a difference.
If you do try them I would let them sit in some tank water in a bowl for at least 30 min to let them open up and get used to the water before dumping them in. It worked for me..