I have the predecessor to the HS5's (HS50m, mostly the same monitor) and they're nice and clean, pretty easy to mix on. A bit light on the bass on the 5's, but nothing I couldn't adjust to when mixing once I got to know them. I'm sure the 8's don't have that issue. Personally, I'd look into the Kali Audio LP6 or LP8. I have the LP6's as my main monitors now, with the Yammies as backups for alternate listening to mixes.
They're probably pretty decent. But a lot depends on how big your space is, what treatment you have and especially (with rear ports on the speakers) how close to a wall or corner you put them. I tend to gravitate more to 6-7" speakers for the nearfield, but no reason 8s can't work if you have good control of the low end in the room.
Yamaha accidently hit gold with the NS10 in the '70s, so if they kept any of the design DNA then they should do you well.
They are one of the standards in the industry. You can trust what you hear from them, and that is what's important. I don't own a pair myself, but I record in many studio's that have them... they are really nice.
I have them to play a digital grand piano with software. They're crystal clear. I'm not an audiophile, but I was able to compare to a few other monitors, and these won hands down.
They're rear ported, so make sure you have a little space to get away from the wall. I have less than suggested, but I don't notice any imbalance.