In the Bryn Mawr Classical Review, Timothy B. Sailors has reviewed the recent Greek-English edition of the Apostolic Fathers by Michael Holmes:
It’s an excellent review which contains good information about Holmes’s book as well as other editions of this corpus. Though he has a number of quibbles with this edition, his overall analysis is a positive one. Even if you are already convinced about the usefulness of Holmes’s edition, Sailors’s review will be worth the read. I purchased Holmes’s edition last year and highly recommend it. It remains close to my desk and I use it almost daily, despite the fact that I own the other editions by Lightfoot, Lake, and Ehrman.
Update: Rick Brannan has also posted some of his thoughts on the review; see here.

How do you like Ehrman’s? I’ve considered buying the set on numerous occasions but I haven’t been able to pull the trigger.
I like Ehrman’s edition, but if you already have Holmes, I’d suggest using the $40 (or whatever) on something else. Both versions have a limited critical apparatus; both have Greek and English on facing pages with an up-to-date translation. For me, Holmes wins the prize because it is one volume and has a similar look and feel to a Greek New Testament, plus the bibliography etc. is slightly more recent.
I’ve used both extensively for an article that is currently under review. I think that Ehrman was at times more open to less traditional translations, which I was a fan of. On the other hand, it seemed to me that Holmes relied heavily on BDAG, which gave it a unique translation or two. Ehrman seemed content with mundane glosses in places where a reliance on BDAG would have really improved things.
I agree with Brandon. If you already have Holmes, save your money.
Thanks for the helpful input, Michael.
Happy to provide my two cents!