I've had an Enve post several years ago. I can't comment on flex because I honestly don't remember. I didn't like the head clamp. It slipped a lot and I had a hell of a time keeping my saddle positioned where I wanted it.
My Ritchey Flexlogic post has some decent flex on it. I didn't like the head on it much either but it worked. I've moved to a suspended post, Kenekt, and love everything about it except the weight. My ass thanks me though.
I've got a Lynskey ti seat post that's got a similar round head design with wedges as the Enve. I don't like it much. Too many loose pieces when changing seats and not easy to microadjust seat position. Lynskey said to torque it to 17-20, which is a lot. It hasn't slipped yet at that torque, but it does at 12-ish if I hit a bump. If a post slips once, then you never trust it anymore. I just ordered a 2-bolt Paul seat post and will swap it the next time it doesn't appreciate my patience with it.
We have the Ergon post on the back of our tandem and the stoker tells me that she loves the ride. It definitely does flex but she claims she doesn't feel any bad behavior. Note that Ergon states these posts are not for off road so I'm not sure of their position for gravel roads.
Actually I have read some articles about tests on this before, and all those seatposts help a little, but the Canyon VCLS is head and shoulders above the rest. Only issue is that if you don't buy it as part of a bike, its 250+ USD.
There are two versions of Canyon VLCS seatposts. The VLCS 2 is the split post and I suspect that's the one you mean. It's also available as the Ergon CF3 Pro Carbon and you may be able to find that post cheaper. However, it's apparently no longer being sold in the US or Canada, though you may be able to order one from Europe.
i would avoid any seatpost with sideways 1 bolt design, they all slip when hitting a bump or misclip during traffic stops. 2 bolt front and back is the way to go, infinite adjustability and no slip
