I am not sure if the links are going to show up right but in yalls opinion what is the difference between all the different double air difusers? They range from $129 to $215 and they all look the same for the most part. They have a hollow base you fill with sand or gravel, pvc type tubing splitting the air to 2 membrane type diffusers. I am trying to buy one and keep confusing myself!!!

https://www.123ponds.com/epmd2.html?gclid=EAIaIQobChMI7u2Zgb-12gIVFdNkCh0p_AYyEAkYAiABEgLG8_D_BwE

http://www.aquaticponds.com/Matala-Dual-...CyABEgJKKfD_BwE

https://www.shopaquatic.com/products/hak...ECABEgK5LPD_BwE

https://www.bjpond.com/product/vertex-xl2sw-coactive-airstation-diffuser/

Check with each supplier as to the volume of water moved per unit at depths same as you plan to locate your dual diffuser. The Vertex unit has the water volumes available. Vertex units have a special built in valving that equalizes the air flow to each diffuser making them perform better in unison than competetors. Some Vertex vendors will sell just the disk membrane and you assemble or mount the disks for a cost savings.