By me responding please don't consider my remarks as 'experienced' in this field.
You and I were looking at many of the same items on eBay, I guess. I passed on the unit because it was a voltage output device, and I have nothing to hook it to other than some WindTrackers that use the 0-5 volts out.
However, you are apparently more adventuresome and with your familiarity with Arduino or Rasp PI, you should be ready to go quickly.
I cannot speak to the unit's invincibility to withstand reverse polarity hookup, so be careful. The little screw terminations however are very robust and make hookup pretty simple.
A couple observations, which may help. I'd feed it with 12 volts if you can. Remember you have to send about 5 millamps, at 12v, up to it, so choose the heavier Belden type cable if you can. 22 gauge minimum. With other types I've had 22 gauge cable run 150' easily. Remember to ground the shield to a ground on your Arduino or the power supply.
The downleads will have a voltage, as you noted, from 0 to 5. I doubt you'll ever have a wind speed which will give you a 5 volt output, something over 150 knots if I recall. And the current is miniscule, so the 22 gauge should be OK for that. If you have the chance to scale the input to the Arudino, and can select up to 2.5 volts, you should fall within the range of most of the outputs you'll get from the unit. And if my experience is correct, the values will be darned close to what you'd expect from a research grade instrument that new costs more than almost every Davis station there is.
With the voltage output, you'll avoid the sticky wicket of having to count pulses for a period and then do math to figure out how fast the wind is blowing. And the shielding will help prevent any induced current, unless you are running a kilowatt ham radio rig near by, especially CW which has been a problem, but then again I seldom run CW and never more than 50 - 100 watts. With the pulse type I have running unless you are mated to a Young translator or Wind Tracker, it seems random neighborhood noise plays tricks on the station's front end and I get occassional 90 mph gusts on calm days, so the voltage output should reduce or eliminate that possibility.
The wind direction will be 0-5 volts for the 360 degree span, so write your scaling code accordingly. I have few with the voltage output, but many otherwise, and they all but one had the calibration sheet with it and when new, they are remarkably linear. The manual says 13.9 mV per degree of indicated output. And it says that 1 meter/second wind which is 2.2 mph is 50 mVolts and scales up above that, so 2.5 volts will be about 110 mph, at which point I'm in the basement under something heavy.
The hookup is pretty clear, with shield of the Belden cable going to a ground, the Positive (12v is my recommendation, not 9v, with low ripple so use a good power supply) + power to the WHITE (they always seem to use white for positive power, not red, dunno why), Power REF is actually the ground or negative of the power supply (not quite the same thing, but close) and is BLACK (which makes sense) on their diagram.
Output Ref (BROWN) is just the signal ground for both the wind speed and wind direction, so that one terminal does double duty for grounding or negative, and both the Wind Speed (RED) and Wind Direction (GREEN) reference or compare against that terminal. So to measure the Wind Speed, you measure from the RED to the BROWN and to measure the Wind Direction you measure from the GREEN to the BROWN. Among all the Young stuff they refer to the ground or non-active terminal as a REFerence. I know on some of the humidity modules I have the REF actually refers to a voltage above ground of 3+ volts or so, and somehow the internal goodies use that to generate a signal that is more accurate, rather than supply voltage. Don't let that last sentence confuse you and if it does, just delete it.
I think you could be up and running in a few minutes.
I have an RM Young 28600 translator, which I hooked up with power supply, reference and WS and WD terminals, loaded about 15 lines of code and voila, I was looking at numbers.
You should do just fine.
Can you let us know if you find my comments in error in your particular situation?
And of course let us know what you have for results and how you are going to display the output or feed it to some wx program with your Arduino or R-Pi?
I assume you got the manual with it or you found the right one on Young's site for the connection diagram? Dale