I actually put my Bones STF 99a (Natural Color) V5s 55mm on my main board to see if they would feel any better than on my rainboard.
The main word I would use to describe them is DANGEROUS. They do NOT initiate a slide easily. I have to really crank my hips and put some weight behind them to initiate even the smallest slide. They're harder to get to slide than F4 97a BUT the MAIN issue with the STF 99a is that once they start to slide, they can easily become ICE CUBES. I'm talking, hydroplaning with no traction.
Its like when people do those ghost-riding boomerang tricks with the board rotating along the ground in front of them... except ALL of your weight is on the board-- RELYING on the board... but the board has no traction to support you.
The margin of error between "no slide" and "no traction" is so insanely narrow. I really can't recommend these wheels for that reason alone. Even reverts are noticeably sticky and require more effort. Which of course when it comes to powerslides, this extra muscle you put into it makes that small margin of error very easy to blast past.
For comparison, F4 97a's grip is consistent. It sucks for sliding, but it consistently sucks for sliding in a reliable way that is never overtly dangerous. For the STF 99a, It feels like I have to put so much extra effort into overcompensating, even for something as simple as a revert. Even just popping 180s, there is less margin for error on the rotation because they stick when you land.
I wish the slide wasn't so bad, because as Xen said, they handle rough stuff better than F4 99a without feeling soft/bouncy like F4 97a. That's a pretty notable achievement, and makes me want Bones to give this formula another overhaul. In general, they are noticeably faster than F4 99a too (something Bones wheels don't get enough credit for).
As for the shape, these V5 wheels have such a narrow contact area compared to everything else I skate. It felt like my board was "on its tip toes". People like to compare Bones wheels to Spitfire wheels by width, rather than contact patch, and I really discourage people from doing that. These things are really narrow at 16.5mm of contact which is equal to Spitfire's absolute thinnest wheel at this size (Classic). Conicals at this diameter are about 20.2mm in contact.
I might give the 56mm V6 a try if I can find those for for $20, but for now, I think I'm putting these on the shelf.
+ Rolls faster than F4 99a.
+ Handles rough streets *much* better than F4 99a, but not quite as well as F4 97a.
+ Feels like a hard responsive trick wheel without the slightly bouncy/muted feel F4 97a have.
+/- Have a deeper muted sound compared to F4 99a and STF 103a.
- Extremely sticky. Hard to initiate even small slides. Reverts require more effort.
- Completely lose traction easily. The margin between the force required for initiation and slip-out is very narrow.
- Less margin of error for board orientation when landing due to stickiness.
6.5/10. I can't say I recommend these. I love everything about this formula except the slide, but the slide is really THAT BAD.
If you're a skate nerd (I use the term lovingly) they are a unique wheel worth checking out on clearance just for curiosity sake: due to being a hard and fast 99a wheel they can handles rough stuff more closely to a 97a wheel. But otherwise, I would say stay away and recommend the (unexciting but useful) F4 97a for a wheel that handles crust.
I wish I got to try the white 99a Easy Streets, because those sound right up my alley. Until then, I guess I just have to wait for the "Experimental Formula" that Bones/Powell-Peralta have been teasing for years now.