I think Dryden's books have a particular style. They are old-fashioned, and strictly avoid the lexicon of the populist self-help genre. With that in mind, they are not for everybody.
REBT provides an interesting framework that is methodical, if complex. You do need to see the book as something to be studied; ironically the problem it addresses may make this impossible. However, should one persist it is a worthwhile and helpful book - I think it is the best on the subject.
This book is absolutely diabolical... It is very badly written and the advice in it is so so... I bought this book instead of other ones of the same topic mainly because the author seemed to have a larger number of publications on the matter so I thought she'd be more of an 'expert' but frankly, this book is really really bad, but unfortunately, I can't recommend another one on self-discipline as I don't know of any other ones.