I use the Butler Creek flip-ups on all my scopes. Almost all of the "see through" kinds, polarizing or not, are going to cut WAY down on the clarity of your optics. Unless you can find photography quality filters to put in front of your scope you're not doing yourself any good.
I don't put them on so much for protection from rain, but for protection from the every day dust, dirt, crap, scratchy stuff that will contact your optics every day they're used. It will only take one time for you to scratch a lens on the way into a stand for you to say "I wish I would have put an $8 cover on it..." From a few years of carting around very expensive camera gear, I guess I'm paranoid.
To me the flip-ups are a necessity, and if you get the correct fit, they won't fall off, and they're in no way intrusive. Only thing is if you have one of the ridiculously big objectives 50mm or bigger, they can be a little hard to flip open with just the push of your fingertip.