We bought one about 6 months ago, slightly unsure because our water pressure is 38 psi, so a little below the required 40.  But someone at the company said it should work perfectly anyways and it does!  There's no issues with the water flow and it tastes great.  No problems so far.  No noticeable noise either. 

When we first installed it it was very slow during the clear out process but once the installation was done and it was up and running it starting flowing normally and we haven't had any problems with the flow speed since.