The black cable is permanently attached to the antenna, so you can't swap it out for a white cable or a custom-length cable. That's too bad, because if you're planning on placing the Winegard high on a window, that black cable can look unsightly running by white walls. (Again, the Mofu Leaf includes a six-foot white cable.) The included 15-foot cable should be pretty workable for most setups, but there can be a lot of a lot of variability in antenna placement, so you may want to estimate how much length you'll need before purchasing it. You can add length to the antenna using an adapter plus another cable if you need to.
While I did a lot of testing with the FL-5000, my results are far from comprehensive. I don't have equipment for measuring antenna sensitivity, so my observations were limited to my subjective experience and my TiVo Premiere's built-in signal meter. Furthermore, all of my testing was done from a single urban location, although I did experiment with different antenna positions.
Caveats out of the way, my main goal of testing was to see if this ultrathin antenna could replace my more traditional-looking antenna, which I have placed on a windowsill angled up. I tested the Winegard in three locations: right in front of where my other antenna is, at the very top of the same window, and lying flat on my TV cabinet, as shown in the marketing materials.
In my specific environment, the FL-5000's performance was about as good as you could ask for, although it can't work any miracles. It registered the same number of channels as my Silver Sensor antenna in each location, but the signal strength varied quite a bit. My instincts were right in that it performed best placed at the highest point of my window, behaving nearly identically to my original antenna. Next best was the same location as my original antenna, where it performed reasonably well, but had significantly less signal strength on all the major networks except ABC and PBS.
If you were planning on simply laying the antenna flat under your TV, I'd think twice. Unsurprisingly, signal strength was significantly reduced on many channels and there was more than intermittent breakup on several channels. In that position it wasn't nearly reliable enough to use as your main TV source.
As positive as my experience was with the FlatWave FL-5000, I have to confess that I'm still using my trusty Silver Sensor as my home antenna. I went into the review fully expecting to upgrade my home setup with a thinner antenna, but it wasn't quite good enough to get me to switch. A big part of my decision was aesthetic; I wasn't able to hide the black wire well, while my Silver Sensor antenna allowed me to use my own white RF cable. And beyond aesthetics, there was still that nagging feeling that the bigger antenna would provide better reception in the long run, even if short-run testing didn't bear that out. (Reviewers have our biases, too.)
But that doesn't mean I wouldn't recommend the Winegard FlatWave FL-5000 (and the very similar Mohu Leaf). In fact, the FL-5000 and Mofu Leaf would be my initial antenna recommendations for beginning cable-cutters: they're much less bulky and allow more placement options than traditional antennas, and because they can be easily installed in better signal-receiving areas, they perform nearly as well.