I have about a thousand miles on my prototype Pacenti rim and I'm very pleased. The rim has the tubeless friendly internal shape like other recent rims. I have been using Michelin 23mm and 25mm tires with tubes so I can't comment on tubeless yet, but I might try at some point.
With my 23mm Michelin tires, the sidewall is flush with the brake track. I think that this will prove to be a good aero combination. The spoke side of the rim is rounded and should be a benefit to that as well.
The rim is welded and machined so braking performance is as excellent, no tick at the joint. My copy is 452g so it's competitive with it's class. I'd rather not have it much lighter as stiffness and durability will suffer.

