For an introduction, I think you can't go wrong with Altland and Simon's (A&S) book. Fradkin's derivations will seem like they leave a lot to be desired, but it's obvious to me that a more experienced physicist would be able to cope with them. For example, if you take a look at both of their presentations on the path integral for spin (as A&S call it), you'll see a stark difference in the clarity of presentation.
Moreover, A&Ss book contains fairly extensive problems with their solutions as well as exercises without solutions, while Fradkin's book does not. For somebody looking for introductory material on CMT, doing the exercises and problems is paramount to building a good understanding of the material.
I also found that A&Ss book contains more direct connection to experiments, either through experimental data or through problems and examples that relate to realistic systems. The vibe you can get from it is one of modelling systems; it helps you start from the very basics of this modelling process while Fradkin's learning curve is not only steeper, but also more detached from experiment (but do note that it also contains realistic systems of course).
I would say that once you've gone through the basic stuff from A&S (maybe the 3 first chapters?) you'll be able to start your journey through Fradkin's book, although you'll again not be able to go through the tougher sections.
