These covers basically turn a spoked wheel into a disc wheel. I understand they may be a little heavier than a disc wheel, and fitting the cover to your rim is extremly important. However my limited budget puts all disc wheels out of the relm of possibilty.
So I am looking for reviews from those that have tried these covers. Do you have any tips about getting the cover to fit the rim, and are there any issue's you had or dislikes. I appreciate all your help, and like I said I'm looking for reviews, not starting a debate as to whether the aero advantage is as good as a disc wheel, there are enough of those threads online.
I use a Wheelbuilder disc cover on my Easton Vista rear wheel. It's a great (budget) alternative to an actual disc wheel.
Although it's a bit heavier than a real disc (I don't really notice a huge difference with/without the cover), it also rides/handles better because it handles just like the wheel it's covering. You don't get any of the disc flex issues when climbing out of the saddle and cornering that you get with a real disc. You also don't get the cool "whoosh whoosh", though. :-(
I had mine custom-cut by Wheelbuilder and have no fitting issues whatsoever. All you have to do is tell them what wheel you plan on using it on (or supply them with the rim depth and spoke count) and they'll take care of the rest. I believe this was $20 extra, which still puts the complete price well under $90. Just tighten the fasteners, and it's snug to your rim. Simple.
It's about a 10 minute job to install the cover. All you have to know how to do is remove/reinstall the cassette. I leave mine on during the tri season. For the price, it's not a huge issue if it's gets damaged. Although, if you're careful, the thing is fairly durable.
The only mod I made to mine was to replace the two sets of the fasteners around the valve with aluminum versions so that I could undo them to fill my tire more easily without worrying about the plastic fasteners stripping out from repeated use.
In my crude testing on a flat course that I've ridden a number of times, the cover is worth anywhere from 1 - 2 mph average speed, depending on the wind. The windier it is, the more it helps.