The RedyTemp system is a nice solution but it has 2 problems.
First you will need an electrical outlet under the sink and in most municipalities you need a permit for that.
Second is that to activate it you need to push a button which also needs to be wired from below the sink to above the sink.
Another solution to look at is the WaterQuick Pro II. It installs at the water heater and is activated by turning on any hot water faucet in your home.
The way it operates is turn on a hot water faucet and then turn it off. Wait about 10 seconds and you will have hot water.
The theory behind the system is the same as the RedyTemp. However it is a lot easier to install (about 1 hour) and if you are good with a wrench you can do it yourself. Otherwise any plumber or handyman can do it for you.
Google WaterQuick Pro II to get more information.