Fray is a ridiculous piece of rotten donkey crap. It's pure, undiluted garbage responsible for nothing but delivering hot trash such as the scythe with all of its half-assed bullshittery and male slayers as well! Yes, if Fray's a slayer then so is Harth! But wait, it gets better. A bunch of characters from Fray look like the Scoobies and it's not a problem until Buffy takes a plunge into that waste dump herself, because apparently season 8 wasn't nearly nonsensical and incomprehensible enough without a time travel story, and you suddenly can't tell her apart from Fray's sister. On the top of that there's absolutely nothing interesting about Fray or her impossibly generic world. Also, Fray is so bad that it outright murdered season 8 sales. Seriously, take a look at the data - readers could deal with zombie Warren, Aluwyn, Satsu, Dracula and giant Dawn but Fray? No, Fray was just too much. That's how bad it is.
Do I recommend it? Of course I don't. There's only one reason to read Fray and that is to better understand season 8 but since season 8 doesn't make any sense anyway there really is no point. Skip it.