The breeder is probably offering the deals because she's
also afraid nobody will want him.
6oz less is a significant stunting in growth for such a young kitten. Nearly 1/3 less than the healthy littermates (unless they're a really big breed - most kittens will be about 1.5lbs at 6 weeks). That makes me think he is a kitten who has general failure to thrive and/or a major medical concern - there wouldn't be a size difference with an innocent heart murmur. He potentially has numerous medical concerns, which may or may not even be treatable and/or allow a normal lifespan (or even adulthood, depending on severity of the underlying issue). That's a big ask on anyone - hence when the breeder is effectively offering to give him away. If you take him, you just need to be realistic about his future and have an idea how far you are willing to go with whatever issues emerge, and understand that you are giving him a great life for what might not be a long time.
And I agree with making sure any pet insurance includes any/all preexisting conditions - most don't.
An “innocent kitten murmur” is usually a grade 1-2 out of 6 and is outgrown by 6 months. A murmur grading higher than that is less likely to be outgrown and is more likely to represent a defect in the heart, which may or may not be a problem, but will need an echocardiogram and evaluation by a cardiologist to determine diagnosis and prognosis. Insurance is a moot point since it will be a preexisting conditions that will be excluded.
I agree with all these.
There is a sense of
urgency placed on this exchange
by the breeder. The breeder says she wants to place the healthy smoke colored kitten up for adoption next week as she has people interested in it. (Understandable, kittens can double in size in no time. And there is a sweet spot for adoption time.) Yet, she feels no sense of urgency to get the stunted kitten properly examined by a vet who can professionally diagnose the intensity and location of the heart murmur. In fact, that exam is being put off for a month, at least!
Is there only ONE vet in all of WI who can run the test or echocardiogram? This is for a test, not treatment. I can understand one wanting to wait for
treatment from one's usual vet. Wouldn't a specialist be the one doing an echocardiogram (or whichever is the right department for the right tests,) NOT a regular vet.
And one can be told a preliminary, "The heart does look small, but doesn't appear to have any major abnormalities. Of course, your vet will discuss the results with you." Versus, ". . . There does appear to be some abnormalities. You definitely need to discuss this with your vet and possibly a cardiologist. I can't give you any more details." (Something like that. I had a radiologist who was able to assess a previous situation I had. She didn't just run the machines and take the photos/x-rays without some knowledge of what she was shooting.)
So, WHY an urgency for one kitten who MAY have possible interest? Yet no urgency for the kitten in which there is definitely interest by Robin?
It MAY be that she doesn't want actual details yet that she'd be forced to disclose. She's willing to make a vague "heart murmur" as a warning to any customers. And she may be hoping that you will just fall in love with a kitten so much that she suspects has real problems, and will then take it off her hands and you become the ones to deal with the problems. Whether it means putting down the kitten or living with it with all it's upcoming medical problems.
Be careful what this BOGO "deal" is possibly about that's no deal for your heart IF the worst happens and way too soon.

And for all of you who said, "Someone has to take the kitten to care for, even with all the problems." NO they don't.
And NO, ROBIN shouldn't be guilt tripped into being the one to care for that kitten if she wants a different kitten. Just because she learned of that kitten doesn't OBLIGATE her to be the one to care for it. Robin deserves a healthy kitten if she wants that instead. No shade, no shame in wanting that for herself and family.
There are hundreds of HEALTHY kittens and cats overcrowding shelters which will be euthanized this month due to overcrowding. Cats which would have lived long, healthy, wonderful lives if given a chance. There is no dearth of adoptable cats. So, no, one doesn't have to take an unhealthy kitty one learns about, unless one wants to be the one to care for it. (We already know why Robin wants a specific type of breed. My example wasn't about her getting a shelter cat.)
Robin, maybe it is enough for that kitten that you loved it from afar for several days,

before it goes on to whatever fate awaits it. (It could also go to someone totally up for the challenge of taking care of it, with no doubts or hesitation.) You knew it exists. You gave it more love than those healthy kittens in shelters, or on the streets, got this week. That can be enough.