Based on the preface, can you provide a summary of the key literary works about Gurus and their distinguishing features?

According to the analysis in Chapter 0, there are a few key works. The 'Thorale Guru Charitra' by Shri Saraswati Gangadhar is an old, detailed, and widely studied biography. Its modern counterpart is Annasaheb Dabholkar's 'Shri Sai Satcharita,' which is also exceptionally detailed. In contrast, Shri Dasganu Maharaj's two biographies, found in Bhaktalilamrut and Bhaktisaramrut, are praised as excellent and graceful but are noted to be very short. Another scholarly work by Shri Samarth Sadguru Vasudevanand Saraswati Maharaj is mentioned, but it is considered less famous and is placed in a different category because the Guru himself was the author.