I am on my second XD-4. While I love the fit and light weight, there are a few things about it I do not like.
The visor bill on my vibrates pretty bad when I am sitting on my GS. If I stand in clean air, it is better. I have even tried sticking wheel weights on the underside right at the front where it is thinnest. No joy. This has been the case with both helmets. If the material were just a bit stiffer, that would probably fix it. To be fair, not everyone has this issue apparently.
I get a NASTY whistle on the helmet somewhere around where the bill meets the helmet shell. Adjusting the bill does nothing. If I turn my head at an awkward angle it will stop. Even though I wear ear plugs, it is still very annoying at any speeds over about 35-40 mph. Looking online, it would appear that some folks get this and some don't. It does not matter which bike I ride, standing or sitting.
I wish the visor could be changed with less effort, more like a Shoei. It is a pain having to disassemble the bill mounts to change or clean the visor. Also, the visor does not clear well in rain, even when I get in the wind flow and turn my head to the sides. I am not sure what is up with that. All of my Shoei's cleared really well. It does not fog, it is just the spray on the outside of the visor that is a problem. It is bad enough that I try to avoid riding in rain if at all possible.
The helmet does vent pretty well when it is in the air flow. Sitting behind a big screen, it is going to get warm. That is the case with most helmets though. When it is venting, it is not that loud, but I wear ear plugs so my view on that may be skewed. I have a SENA 20S installed with the speakers mounted in the helmet. I have to keep it at full volume if I am at highway speeds, but it works okay up to around 75mph. On back roads and dirt roads, it works fine. There are pads with the 20S that let you adjust the distance between the speaker face and your ears. The 20S clips to the side of the helmet and I am using the boom mic that bends around underside of the helmet and has the mic right in front of my mouth.
I've used the helmet in temps in the mid to high 20s F and also in the 105-110 F range. When the vents are closed, there is still a good bit of wind up the neck/chin area and on the back of the neck, but not really any worse than any other helmet I've used. For the cold, my solution is a Klim Balaclava that goes down inside my jacket and I can pull the opening up over my nose leaving only my eyes exposed, I can leave my eyes/nose exposed, or the whole face. This makes a HUGE difference in comfort. In the heat, if I am on my GS, I either have to stand or occasionally lean out from behind the big windscreen to get some air through the helmet. On my KTM, I get plenty of air through the helmet.
I have crash tested the XD-4. I had a nasty high side on some ice in Utah while riding my KTM 530 EXC. After a bit of flying, I landed on my head. The helmet had scratches across the top from one side to the other and some chips in the paint. It took me a few minutes to catch my breath, but otherwise I was fine. My neck and shoulders were sore, but I did not experience any concussion related symptoms beyond a mild headache that went away after a few advil. We were in the middle of no where, without any cell service, and I had to ride it out. I was able to do so without any issues. I have not tested it on pavement... I'll let someone else do that
I think if I were in the market right now, I might try a different helmet, perhaps a Shoei. It is not that the XD-4 isn't a good helmet, but just that I'd like to try something else just to see. I might end up going back to it later.