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It's really hard to say about the noise as those sort of things seem crazy subjective, but I reckon I'm more sensitive than most to noise but as it's only on for short bursts I can pit up with it. We have it under the sink and I put some noise dampening stuff in there and it helped. The sound of our dishwasher filling is louder than the pump anyway so that's not an issue and generally if the living room door is closed it's never really an issue.
As for the cost of use there's no way it doubles our electricity bill, I couldn't tell you how much it uses but I haven't noticed any real impact on bills.
We've got one of these, it works great but they are a noisier than advertised. We got it when we had the loft converted and get 12l per min when we were only getting 5ish.
We're hoping it'll be temporary as Thames water have upgraded (or in the process or upgrading) the mains inlet pipes round here.
Don't know if it's the same everywhere but here if you've got a small plate flow is shit because of old pipe and if you have a newer Thames water one you've been upgraded.