Dangers of Inner Fire Meditation?

[BlueBuddha]

The Bliss of Inner Fire, by Lama Thubten Yeshe

I have read on other forums that it's dangerous to practice inner fire without a teacher, is this true?

Could someone please tell me what this kind of meditation is about, and why it could be dangerous?

Is it true that this kind of meditation can bring about enlightenment much faster than other meditation practices?

Has anyone you know tried it, or have you tried it yourself?

and..if it is so powerful, why haven't I heard of this before?

Thanks in advance for your reply(s)