In this comments of How many elements can you focus on during worldbuilding? a conversation arose about the usefulness of non-genre savvy beta-readers.
Another question Are "non-readers" useful beta readers? discusses the topic more broadly in terms of how useful non-readers are as beta-readers.
Should beta-readers have experience in the genre of the work they are reviewing? Are there advantages to having a non-genre-savvy reader review your work?
Both are useful.
Someone who is genre-savvy will already know the rhythms and tropes of the genre, and can advise you about extra things to add, or say "This theme has fallen out of favor in the last two years," or point out "So-and-so did this already, so don't borrow too heavily."
Someone who is not genre-savvy will be able to tell you what needs explaining so that you can capture readers outside your genre.
You need to figure out who the audience is going to be.
If you're primarily aiming at a genre audience, or at least expect them to be the majority of your audience, your beta reader demographics should probably be weighted toward that; they'll have knowledge of the genre, can identify issues specific to that genre, and give you a sense of how your story may appeal to that group of readers. The "outsiders", as it were, can quickly tell you if you're descending into the trap of unexplained references that you have to be a long-time fan of the genre in order to understand or use too many tropes that can't be understood by people not conversant with the genre. They'll also tend not to be blinded by the things genre readers have long-ago accepted and don't even bother to notice any more, but which might be useful to look at.
If you're writing primarily for the out-of-genre audience, then the proportions should be reversed. The "insiders" are, essentially, acting like experts you might get to review, say, a story about a soldier if you've never served in the military.
If you're not sure, you should at least have a mix, but you have to be aware of what each is bringing to the table, because each will have their respective strengths and weaknesses. To use a film analogy, imagine that you had two reviewers watch a film, one a writer, the other a cinematographer. One might have a greater appreciation of the dialogue and the story, the other of your composition and visuals. If you were asking them to look at a very character-driven bottle film (basically, everything takes place in only a few sets, perhaps even just one or two, for instance 12 Angry Men) where the camera work was fairly basic and relied primarily on set shots, then you'd want to pay more attention to the writer when it comes to the overall film and rely on the cinematographer for advice on perhaps altering a few shots. If you're doing a massive Michael Bay-style summer blockbuster action movie with characters defined by dramatic shots and their physical actions rather than anything they say in service of a pretty basic story, then the camera person is the one you want to pay the most attention to while the writer might have the odd suggestion for making dialogue a little less clunky.
I wouldn't want a non-reader, I definitely want somebody that likes to read and gets immersed in fiction.
But then, I wouldn't really care if they are a genre expert. A good story is a good story, almost anybody that reads novels will be able to tell you the most important thing a reader can tell you: Where they lost immersion, what confused them, what seems clunky, or overdone, or drags, or seems pointless to them.
My approach with readers is to tell them the reason I want them to read is not to get praise. I don't want them to worry about my ego, I want them to show me what to fix before I send it to an agent or publisher and get rejected for it. More than anything I want negative feedback. If the sex scenes are flat, tell me. If the action scenes seem contrived (because of course they always are) I need to fix that. If any character seems to do or say something too stupid, tell me. If they ever find themselves saying, "How convenient!" or "What a lucky coincidence!" in the story, they have spotted a deus ex machina that I need to fix, and make the "coincidence" less obvious, or better justified.
Anybody used to reading stories and willing to read your story is extremely valuable, in this respect. Get all you can. Don't get hurt when they actually have negative feedback. (Also, don't feel obligated to fix something you are certain is right.)
If you can also get somebody that likes reading your particular genre, great, but I wouldn't turn anybody down that's willing to read, and I believe will actually finish the book.
Readers with genre experience are better because they know the genre tropes and how a book in the specific genre naturally flows. With that in mind, if you are planning on publishing, I recommend getting experienced beta readers who know what they are doing.
