I fished Tenkara with my brother last year for trout in NC. It was fun but not my first choice. A really effective method though, especially on heavily fished waters. Current as cover definitely is a plus as most every water we fished was crystal clear and trout would spook easily in still waters. The trout really use the current to hide in on the skinny waters. Also, anytime there was a dark patch on the bottom a trout might be in it. We caught some pretty hefty trout too, had to chase a few and also had a few pop the light tippet.
I definitely believe it would be an effective method to catch smallmouth but again, I'd rather cast poppers or streamers to them as a first choice.