SMu DoFollow has many DoFollow Options (Manual or Automatism) and included URL Validator (Manual, WP-Cron or Cronjob).
This plugin has 2 diffrent functions. The First, two diffrent Link functions: the automatically and manually-set status. First, the Plugin checks if there is a manual-set status, which needs nothing on performance, because its connect to a very small database which contains small data.
If there is no manuall set status, the automatism is checking the comments table for the amount of comments of the user. If you have a very large number of comments, you can feel a very small decrease. But if you really have more than ~20'000 entries, you will choose a Cache Plugin anyway.
The Secound is the URL Validater. This can made manually, via Cronjob or automatically over
The manually needs a little bit of time but will not decrease performance for the readers, also the cronjob.
The best way for big blogs with a hugh amount of links is the cronjob.
Yes, there is are 2 new tablse added in the wordpress database with the name
wp_man_dofollow2. This Databases contains the information about manual set DoFollow/NoFollow Users and the time/status when the link is checked the last time.
The first table
wp_man_dofollow content is a mailadress and an ENUM(yes,no) value.
The secound table
wp_man_dofollow2 contains the URL, Status and Lastcheck time.
Both databases doesn't need a lot of space and performance to generate the needed functions.
No, otherwise I would fix it :) Please test the Plugin and report every bug or feature request to me on IT Blögg - WordPress Manual DoFollow Plugin