Got a B17 narrow on my tourer that I use nearly everyday. Very comfortable with or without padded shorts [not tried it naked yet, but will report back accordingly].
I did have one on my hardtail for a while. It was comfy, but to be honest it took a proper battering and despite the proofide and the use of a rain cover, after getting soaked wet through and covered in mud/grit three times a week, it soon became overstretched, and an eyesore too.
Would I recommend one …
For a tourer/commuter/fixie most definitely, for a road bike possibly, off road bike – no.