I personally love them. I have an odd fascination with anything factory FDE, and will often pay a premium to get it. If it's available in factory FDE, I have to have it in factory FDE. That being said, I'm not spending $1000 on a used Gen 3 G17 just because it's FDE - that's crazy talk. If someone had a Gen 4 G17 in FDE they were willing to part with for a reasonable dollar value, I would be all over it. They're not overly common, and I was busy buying a Gen4 G19 when Dlask was selling the G17's, so I missed the boat.
Bradley