I know this thread is cold, but it comes up when you Google Erin Boxers, so I feel I need to speak up.
Our 3 1/2 year old bitch came from Erin Boxers and has been bred by them. She's a sound dog, with a temperment that can be described word for word by the breed standard. I agree with the previous poster who mentioned they breed on the larger size. My girl is big for a female.
You can't judge a breeder by a website. Greenfield Puppies has a lovely, slick, well done website with cute little bios about the dogs. They are brokers for puppy mills and backyard breeders in PA. Cardale Boxers, on the other hand, has no website, but is owned by the President of the NJ Boxer Club.
Jack O'Brien breeds sound dogs and cares for them well. Jacquet's (Rick Tomita's) Bravo was the foundation stud for Erin Boxers, and, in my experience, Jack is very careful about who he breeds. My girl was bred with a Cardale Boxer, whose father was a Jacquet. Jack is regularly in touch with Rick Tomita and is well known by the community of reputable breeders in NJ.
It's been my experience, through training with and getting to know some breeders in NJ, that many of the reputable breeders in the state are older. Jack and Mary are middle aged, Carol Brower is of age to be retired from her full time job. These aren't people of the information age. They've been working with dogs for a lifetime, however.
If you're looking for a pup, contact the state boxer clubs in your state and neighboring states. Talk to the club officers. When you call one kennel, ask them if they've heard of/know anything about the other kennels you're contacting. It might even be worth it to talk to some well known trainers in your area, if there are any, esp if there are any behaviorists. They know what dogs they've seen with problems.
And, pick up the phone. There's a lot of communication lost in emails. A hesitation when answering a question, a tone of confidence or enthusiasm when decribing their dogs - these little things tell you something about the person you're talking to, and these are the things lost in email.