There can be downsides to the permeate pumps, but not many.
Installed with a standard hydraulic shut off valve (ASO) you won't see any issues but you won't get much in the way of improved storage pressure. You will just see improved product/waste ratio as the pump negates the back pressure from the tank. The downsides are the periodic thumping noise and the added complexity of the extra tubings and fittings.
Installed without an ASO valve the permeate pumps will cause some TDS creep and bleed high TDS product water into the storage tank each time the system stops and starts. This will mix with the low TDS product water and raise the average up somewhat. The amount will vary on usage behavior but it's a noticeable TDS bump for most users.
Installed with a standard hydraulic shut off valve (ASO) you won't see any issues but you won't get much in the way of improved storage pressure. You will just see improved product/waste ratio as the pump negates the back pressure from the tank. The downsides are the periodic thumping noise and the added complexity of the extra tubings and fittings.
Installed without an ASO valve the permeate pumps will cause some TDS creep and bleed high TDS product water into the storage tank each time the system stops and starts. This will mix with the low TDS product water and raise the average up somewhat. The amount will vary on usage behavior but it's a noticeable TDS bump for most users.