Tosh is referring to the domestic RO filters, mostly used in homes for drinking water.
You can add extra membrane housings to these to increase the GPD.
They aren't as fast or efficient as the 4040 or 4021, but quite a few window cleaners use them, as do aquarium enthusiasts, and leave them on overnight to fill their tanks.

If you're looking for something more efficient than the Merlin, then I'd recommend a 4040 ro.