All four of them are outrageously greebled and detailed (which isn't a bad thing, mind you), making them feel more like anime characters than Toa. I'll go through each of them one by one.
Individually I can see the designs working, however when put together the MOC somewhat falls apart. The legs are far too thin to look like the Toa can even stand up, however the forearm design is original and looks cool, however being the only huge block of silver on the MOC (save the thigh) it looks a little out of plane. The silver being more evenly distributed would help greatly. Overall, good but could use some work.
The proportions of this guy make him look a bit like a young child, I could see slightly longer arms working. The greebling on the legs is a bit overdone compared to the relatively normalized arms. The waist wouldn't hurt to see some slight bulking up, but the true greatness of this MOC is in the head, because the giant cheeks of Tahu Nuva's mask look normal. My review is the same as the last MOC, though this one is a little better.
A bit easier on the eyes than the last two, this one manages to so far be the best. The leg design fits well with the rest of the MOC, and the only con I see is the Nuva shoulder armor on the rear end not fitting in the rest of the back, being too thin. I have mixed feelings on the artwork for this one, since it doesn't do the MOC justice, considering how abnormally large the thighs are compared the the actual thing, and the head being too small for my liking. As for my final thoughts on the MOC itself, definitely the best one.
The name is a little interesting, being a mix of two Kanohi masks (those being Hau and Kadin). Haukadin himself could really benefit from being taller, in fact maybe switching core designs with Gahakida. Otherwise he is the least interesting of the four, looking like a revamp of 2016 Lewa. The artwork of him is what I would prefer to see (at least the left side), as it makes his height "correct" for what normally Toa of Air have. While not bad by any means, I would say this one is the worst, or the weakest of the four.
Heavily stylized, complete with flashes of color and a load of editing, the Toa Seika team manages to be some of the best collective MOCs of 2017.