To be honest, I am trying to learn formal QED, and this text is 'feeding' well. Heitler comes up with the goods..you feel you have actually covered some topic-(rather than some 'lite' or cryptic version). Having said that modern criticisms would be the usage of 'old' vector operations notation (minor taste criticism-you get used to the use of '[ , ]' for vector products for example); and also omission of 'Feynman diagrams'. However the additional material (to the 1934 edition) published in this reprinted 1954 edition gives reference to Feynman and Schwingers work prior to this date.
For THE treatment of quantum bremsstrahlung theory (first approximation), here is the most oft quoted reference (with maybe an option on Kramers 1923 'Bohrian' quantum paper)and arguably the most relevant. A must if only for this. Like most books written around this time in Dovers catalogue, it is well written, readable, and precise in the analysis- skipping math steps where truly reasonable. A gold mine for those of us trying to get to grips with the subject of the title.