In the early days, I understand that Baidu and Yandex were both known for excessive crawling with very little value for English sites, but those days seem to be gone now.
In those early days, I blocked both search engines, but now I allow them access to my site. It appears that both have picked up on my sitemap and are indexing my pages. I have also noticed an increase in traffic from these search engines putting Bing to shame, so I have no complaints so far.
Are there any statistics to demonstrate the value of allowing these search engines, either based on AdSense conversions or bounce rate, for English-based sites?
I am not looking for personal opinions on these search engines, I know that opinions can run strong and deep and I fully understand that. I'm just looking for metrics based on experience or from credible sources to indicate how worthwhile allowing access might be now.