jonisonvespa:
can i just use the output from it (2.5 to 4.5v) without any other circuitry straight into an analog input?
Yes.
jonisonvespa:
In the spec sheet it quotes Rl (load resistance) should be greater than 2k should there be a 2k resistor to ground?
No. The input impedance of the Arduino is >2K so you should be able to connect the output directly to it. Just hook "5V" to +5V, "0V" to Ground, and "OUT" to an analog input pin.