If you are at all inclined to get all of Plato in one volume then you are well advised to get this volume, for lack of viable alternatives.
The translations are a mixed bag. Cooper had little choice except to take over Grube's translations which inaugurated Hackett editions of Plato. While Grube delivers idiomatic English, he's inaccurate on so many key points that he will simply lead you into dead corners. (Instructurs should seriously avoid him in classroom use. There are worthwhile Penguin volumes of "Euthyphro" and "Republic".)
That said, there are real gems in this collection: Burnyeat's "Theaetetus", Frede's "Philebus", Gill's "Parmenides", Zeyl's "Timaeus", Reeve's "Cratylus", Rowe's "Stateman". But if you are a real fan of (any of) those, you should seriously consider getting the individual volumes (also by Hackett) with their substantial introductions (all of them highly recommended) woefully if understandably omitted from this volume. (Why can't there by a Norton Plato? 3000 pages with all of the individual Hackett's... I know, the market.)
Apart from this alternative (or complementation), you should also consider getting or borrowing items of the Clarendon Plato series: Gallop's "Phaedo", McDowell's "Theaetetus", Irwin's "Gorgias", and Taylor's "Protagoras" - philosophical commentaries and translations which have no superior (not so happy on Gallop, but you'll have to avoid Grube's "Phaedo" anyway).
A final comment. If you are new to Plato, Cooper's volume can be a pleasure to start with. Begin with the first "Alcibiades" and the "Symposium" (both beautifully translated here) and then read Cooper's wonderful introduction to the volume. I very much doubt you'll ever live life without Plato afterwards.