Just a few initial thoughts on the Arx XL3 from first-run setup and testing.
The instructions, as mentioned by another reviewer, are quite spartan. Really, they're just a few lines on a slip of paper. Fortunately, the instructions do include the most important part - the tent is designed on a colour-coded basis. The "red" (well, kinda purple) ends of the poles go into the grommet holes in the red body tabs, while the black ends go to the black tabs. Same goes for the fly - red buckle tab to red, black to black. This even remains true for the footprint (which is not included, but available separately from backcountry), so setup really becomes very straightforward. The poles are nice, but I do have durability concerns about the carbon brow pole due to owners of the Arx XL2 reporting breakage problems. In a stiff wind I could see that pole being put under a fair amount of stress. So far so good, though, and I've never had a tent with carbon poles so I don't have much experience in that area. The brow pole pushes against the fly fabric at the ends, and since it's stressing the light (30D) silnylon a bit, I can see how this could lead to moisture passthrough. I will likely sew and seal a small 2-layer patch of 70D silnylon onto the contact areas to mitigate that, although just applying some silicon-based seam sealer to the area may do the trick as well.
The tent body is nice and roomy for two people and gear! (three people might find it a bit snuggly) The bent-pole design is really good at opening up the headroom, so sitting up for a game of cards is nice and comfortable - between the large interior space, the mesh walls, and the white fly, this is probably the most open-feeling 3-person tent I've been in. Vestibules are of average size (great for boots and smaller packs, larger packs would perhaps be a bit tight) and the mesh doors can be opened nice and large. The vast amount of mesh should make for excellent summer ventilation - although that would also make it rather chilly for early and late-season camping. The top vent is a nice addition, but it has to be opened/closed from outside the tent due to its location above the main body.
Unfortunately, as mentioned by other reviewers, the mesh gear loft is comically useless. It's tiny and is oddly angled, so anything you put in there is going to immediately fall out. A slight redesign (deeper mesh, relocated attachment points) would make this item usable, but since there are mesh side pockets built into the main tent body I'm not too sad about leaving the loft at home.
Now, the specs say "no" for the Fast-pitch option, but upon erecting the tent I was surprised to see that the fly has a number of Velcro tabs designed to attach it to the poles independent of the tent body, indicating that a Fly-only+Footprint setup was possible. A little fiddling later (and again with the help of the handy colour-coded grommet tabs on the footprint) I had the XL3 free-standing and secured without the main body. Anyone attempting this will want to guy it down well, as a stiff breeze picked up and really tugged on the fly. Also, the footprint does not have the clips for tensioning the fly that the main body does, so the guy-outs become doubly important. Setup in fly-only mode wasn't nearly as easy as using the main body, but quite doable, and likely fairly easy if you have someone helping you. I also suspect it's quite possible to (in the case of setup in heavy rain) to set it up as Fly-only+Footprint first and then erect the main tent body underneath the fly, thus keeping the main body dry. The reverse should also be possible, for situations where you are taking it down in the rain. That's something you'd definitely want to practice in the backyard first, though!
So, initial impressions on setup are mostly positive. Things like the silly gear loft design are knocking it down to a 4-star tent at this point. That said, for $150 one could do a lot worse for summer backpacking. I love how light it is for a full-featured 3-person tent - split between two people it's counting for only a few pounds per pack.