Well, after a lengthy decision process on the rims for the Nature Boy cross wonder bike I changed my mind at the last minute.
I chose the Notubes Alpha 340 rims based on the recommendation of a fella at Stans and a few reviews online. Stan's tech support staff will say all of their rims are most excellent if you call them, btw. For whatever reason I researched the 340s a bit more this weekend while I impatiently waited on the wheels to be built. I was not happy with what I found.
Apparently, the bead hook design that makes Notubes rims so awesome on the mountain bike side was changed to suit the new Road Tubeless stuff. I found this post detailing some odd spoke tension changes that occur to the 340 rims when a tire is mounted on them sans tubes. In short the tire compresses the rim causing spokes to lose tension. When spokes lose tension nothing good comes from it.
Also found this in some comments to the excellent cross tubeless primer from the guys at cxmagazine:
yes, you can run rim brakes on ZTR 355 29'rs. we have literally sold hundreds of them. you might have some inconsistent braking til the black anno wears completely off, but its really not a big deal. its a pretty short brake surface though, so use short pads and just watch over the wear a little closer. There is not a better tubeless option/rim in my opinion and we've done tubeless since the beginning. you'll have a great experience with it. Dont bother with the 340. The 340's we were real excited about when they first hit the market. We bought a bunch and immediately started selling them. EVERY single rider we put on them (130-190lbs) had burping issues. We had guys that blew all the air out and people were getting both upset and disappointed. We put two layers of yellow Stan's tape on them initially. That way if they went road tubeless, the high air pressure wouldnt blow through the tape. A second layer is not a bad thing for cross either as a tight clearance between tire and inner rim diameter tends to be a benefit. Not only did we have different heights and weights of riders trying these out, we also had them all trying different air pressures and there was plenty enough people to cover both aggressive riding technique and softer technique. The only couple of things that made these rims solid was higher pressure and the thick Stan's rubber rim strips we started using. Both of these options were bummers to the people that got these rims. Each one of them was excited to have a rim that was both lightweight and to be able to utilize the benefit of running low pressure as we've come accustomed to.
The big bummer now...... Stan's discontinued the ZTR 355 29'r rim a couple of months ago. Ive tried to find them everywhere, but all suppliers are out of stock. so, our limited stock of this rim will not take us even to the beginning of the CX season.
if you find em, buy em. I dont know of a replacement for it yet. Hopefully they bring the original bead seat technology to the Alpha 340 and we'll be very happy once again.
I was able to bail on the 340s at the last minute and am going to use the Arch ZTR 29er rims, which should be the most badass, durable, tubeless cross rim available right now. This is what Cyclepath, a shop that does lots of tubeless cross stuff in Portland recommended to me. The rims are primarily for disc brakes but stop fine with rim brakes after the ano wears off and I can also run 28c tires WITH tubes to whatever PSI the tire is rated to for commuting. I will be using either PDX Crusades or Michelin Mud2s tubeless for cross with Stans juice. Muuuch better feeling about these wheels with the Arches. Now I just have to wait... Some more.