Rick Brannan mentioned this series in one of his forum entries recommending it for Logos (and demonstrating that Logos doesn't 'play favorites' internally I guess).
Anyway I SLOWLY got all 6 volumes. I've written about it before. Here, I wish to recommend it AGAIN mainly because (1) it's not in Logos and (2) it's no longer published, is not public domain and is really touch and go trying to find all six volumes.
So, if the apostolic fathers interests you, I STRONGLY recommend you fish Abe Books and Alibris for the series. Four of the books are reasonably common. Trying to find Polycarp/Papias was a little harder. And Ignatius was a REAL PAIN (the copy I finally found was from the Lexington Theological Seminary library; I wonder why they let it go?).
I suspect as the series was released over a six year period, the later ones were not subscribed as much as the earlier ones.
Why this series vs others?
(1) It's VERY CONCISE but PACKED. Each author apparently was given a set number of pages, so each appears to have 'stuffed' as much as they could into each one.
(2) Grant (the editor) allowed the other authors the freedom to literally disagree with each other (and they do).
(3) 'Commentary' and notes is pretty extensive; maybe 2/3's of each page. Easy to follow.
(4) Used copies are CHEAP. Typically $10 or so.
(5) My impression is they're much more balanced in treating the various views. I also have Hermenaia for Didache, Ignatius, etc and get a little frustrated with the heavy bias that shows up (in Hermenaia).
Soooooo ... don't wait too long. The libraries seem to be unloading. These things disappear.
(I'd put this in the suggestion forum but Rick already knows its value obviously.)