I've got a 10' 4wt TFO BVK. I like it for many of the reasons you mention -- longer reach, easier mending. Its great for nymph fishing, especially on bigger water. However, I have broken it twice (over a few years). TFO has a life-time, no questions asked warranty with $30 fee and pretty fast service, but it's still a pain to break a rod.

I cast quite a few 10' rods before buying the TFO and would offer some general observations ...

10' rods are heavier. That might seem obvious, but the actual weight difference and the added fatigue from casting / rod handling all day might not be so obvious. The extra weight and length also makes it more of a challenge to balance the rod with a fly reel (I ended up putting a Konic 2 on mine rather than the Velocity 1.5 that I had intended). In any case, check the rod weight and if possible, string up the rod with the line / reel you intend to use and see how it feels.

Quite a few guys I know are going to lighter line weight 10' rods. So rather than a 5 wt or 4 wt, many are going 3 wt or even 2 wt. My buddy got a 10' 2wt Sage ESN several months ago and he loves it. He uses it for small and large stream fishing and both dry flies and nymphs. If I was doing it again, I think I'd go with a lighter line weight 10' rod.

It seems to me that the manufacturers are pushing the envelop with the rods. As the rods get longer and they try to keep down rod weight and maintain faster action, the rod walls get thinner and more fragile. Breakage with 10' seems to be more common. I'd make sure the rod has good warranty service.

A couple of minor points ... They are harder to transport -- my strung up 10' rod fits in my RAV4 but just barely. The extra length makes it more of a pain to clear iced up guides.

All that said, I'd still get a 10' rod.