I have been in Mysore since Nov 12, 2012 and have been taking Ashtanga classes at Mysore Mandala the whole time.
I have not been involved in the Teaching Training held at the school, but my teacher, M. V. Chidananda is the same person taking the course. I am still a beginner and have just been working on my practice and learning the primary series.
The Shala has moved recently and is not the same as the one shown on their website.
It is difficult for me to comment on Mysore Mandala as I have nothing to compare it to :) - However, it is quite small(20 people max in the Shala), the teacher is a wonderful man, very patient, elegant, speaks excellent english and his knowledge and Yoga Practice is incredible. The people running Mandala are very nice, there always to help you out and the cafe inside serves good food at reasonable prices.
I am leaving next week to head to Sri Lanka, but will be returning in April to continue my studies with Chidananda.
There are 3-4 other schools in the Lakshimpuram area of Mysore that are held in high regard.
Please let me know if you have any other questions as I may be able to help you out.
I don't think you would be disappointed with Mysore Mandala, but I think alot depends on your level of Ashtanga and wether you actually want to teach or just would like to improve your knowledge and practice.