I have the 'Big Book of Homebrewing', which has a similar section of 50 clone recipes. Can't claim extensive experience with those recipes, but I like the book enough that the 300 one is on my list.
I have the BYO magazine with 250 clone recipes (extract and all grain). They've all been good. Sorry, I haven't read the one with 50 extra recipes. It sounds like an add-on to mine so it's probably worth owning. My magazine cost $10.
Yeah, I have since purchased a copy. Some overlap with the 'Big Book', and I think it really is 50 more recipes than the previous 250 recipe version. Lots of interesting stuff. If you have one of the 150-200-250 versions, probably not worth the purchase unless you are running out of ideas - I guess the 350 is a couple of years away.