Lal Kitab is one of the branches of Vedic Astrology like KP System, Jaimini Astrology, Tajik Astrology, Nadi Astrology etc. I mean you can judge a kundli (birth chart) using various different methods and Lal Kitab is one of them. Lal Kitab method of birth chart assessment has been developed by Late Pt. Roop Chand Joshi. He has written five books all by the name of Lal Kitab and hence the name. The first book was written in year 1939 and the last & the fifth book was written in 1952. Lal Kitab is famous primarily because of its easy remedial measures. Lal Kitab talks in details about the remedies (upaya) that one can perform for various problematic planetary positions in a birth chart.
The language used in Lal Kitab is Urdu/Hindi popular during 1939-1952 period and written in Urdu script (Nastaliq). The language of the book makes it difficult to understand and that is the reason there are not many astrologers who understand Lal Kitab. Most of the astrologers use name of Lal Kitab just to make money without any in-depth knowledge of this system.
Lal Kitab remedies if correctly suggested and performed can be very useful. Though as I mentioned not many astrologers have the knowledge of this subject and they suggest remedy based on their half-baked knowledge. Mind you that the remedies of Lal Kitab can also backfire if incorrectly suggested or performed.