I only know the name "Thumb-shift/NICOLA" but have never seen any actual users. The Japanese wikipedia says 親指シフト規格の支持者には一般的なユーザのみではなく、作家やライター、記者・編集者などのマスコミのほか、事務・司法書士など、大量の文書を日常的に作成する職業に就いている人も多い。 "Besides ordinary users, there are also many people who write a large amount of sentences, including authors, writers, editers, and lawyers among Thump-shift supporters", i.e., the site never says "it's popular among them."
According to the results of a survey in January 2007 by Rakuten Resurch, 0.7 per cent of those surveyed used Thump-shift kana imput method.