Aussie,
Your dart screen doesn't look that bad or obnoxious in that pic you posted. I can totally handle something like that...
How easy is it to take on and off? Don't want it to be a permanent fixture on my bike
I can't really offer any hands on experience on how easy it is to remove as I've never removed it.

I would imagine that it is fairly quick / easy as you just have to remove one headlight securing bolt, move the flyscreen bracket out of the way on that side, refit the headlight bolt and then repeat the process for the other side.
Initial fitting was a little more complex as the brackets had to be fitted first then the screen attached to the brackets. Some bending of the brackets was necessary to get the mounting holes on the screen to line up with the mounting holes on the brackets.
A couple of points on fitting the flyscreen. Don't overtighten the screws that hold the screen to the brackets, just lightly tighten them otherwise stress fractures will appear around the mounting holes in the screen over time. Maybe use a little Locktite on the screws to make sure they don't come loose.
I fitted my screen just before heading off on a 2,000Klm trip and by the time the trip was completed the screws protruding from the back of the screen had rubbed holes in the plastic gauge covers. The flyscreen brackets have a couple of little tangs that sit on the headlight brackets and establish the limit of backward lean of the screen so to speak and on my initial setup the screen would rest against the gauges when travelling at speed. I have since bent the brackets a little to prevent this happening but the damage was already done.
I too thought that the screen would removed and refitted as required depending on the type of riding I was doing but I have found that, in practice, the screen has remained as a permanent fixture. This is mainly because I become accustomed to the look of the bike with it on and the benefits of having it on apply to most of the riding I do anyway. That is, most trips I do on the bike involve speeds above 50Mph for part of the trip at least.