Blog Commenting links are excellent to get traffic + to make a viewer base of your own blog especially when you make high quality professional comments. Spammy comments like good blog, good post etc will not bring in any fruit. People claim to have good SERP results even with nofollow links so there is no harm in trying.
Not only will they help you in traffic, but they are used to help index pages. Google will follow them as well as the other search engines, the only thing that it does not do is pass 'link juice" to the the page that it is linking to. The other thing is that it will make your link profile look more natural. You should have a mix of bot do follow and no follow links.
When the traffic come to you, keep it to yourselves. Do not direct your traffic to other people. My friends joke at me with this advise. Well, you may have a try whether followed link or no follow link, which help your traffic better.
I use SEO spyglass to search for blogs with dofollow links. Sometimes the website url is nofollow however if you insert the link in the comment box it is dofollow. Use "NoDOfollow" plugin for firefox to check the links on blogs.
I think it depand from where you are getting the no-follow links, You should comment on high popularity blogs and blogs must be relevant and definatly it will brings large amount of relevant traffic whether it's no-follow or do-follow.
From my experience, blog commenting worked very good before Google Panda update that is before January. Now its not much effective and also making our site to lose rank sometimes. Doing little blog commenting from very good authority sites are still useful. But mass commenting should be avoided.
it wont be much useful as you will not get any seo benefit from may be you can get visitor but i think that ratio would be also very less. so rather you should consider other activity in that timing which are really worth.