I have Fiskars axe, it is equivalent of X17, but from time before they started branding them as X-something.
Fiskars is great when splitting Birch, but mine is too light for knotty pine or anything gnarly, but X25 or X27 costs a lot, welding machine costs more, however I had one already as well as old broken axe head + some random steel.
Axe head is now roughly 10 pounds in weight, I tend to sharpen it so that I could shave with the blade, it does not matter if there are knots, wrist size pieces of wood can be split across (same direction as you usually saw) with single hit, I love it.
Of course that cheap Chinese axe was unusable at first, it took lot of grinding to make edge for it, also cut handle shorter, it is bit under 2 feet long in total now.
Way I split pine is usually so that I take slices out near the bark, then start working from edge around the round, makes great workout with that heavy axe, especially as I put round inside a tire and tire rests on large splitting block that's top is around height of my navel.
That makes it really fast, just hit, move, hit move, hit move, going around the splitting block hitting around the round continually moving.
Next development stage is to add bit more steel, so that I get smooth transition from blade edge to center on both sides, but I need to build up my strength before that, thing really gets me hard workout as of now.
If I split something that is around knee height or less, it tends to split also block that is under the round, that is my best splitting tool now, 1 foot x 1 foot pine round took 2 minutes to work into less than 2 inch x 1ft firewood pieces, but I was out of breath after that, so I really need the workout, LOL.
Husqvarna axes are better than Fiskars in knotty / gnarly stuff S2800 especially, but I have not tried one, costs a lot, Stihl has also similar axes + wood handle ones, just haven't heard from those or seen them on sale anywhere in here, would love to test them all though.
I heat solely with firewood, I warm water with firewood and even cook with firewood, so I get some practice with the axe, I split around 5 cords a year with my axes, mostly slowly grown nordic pine, some birch and spruce.
Also I do some 3ft long firewood because I don't have room to store all the wood as ready made firewood, I use Fiskars splitting wedge for that. They say you only need one wedge of those, that is a lie.
My method is to hit wedge to end of log, turn log so that wedge is at bottom, lift log up and slam it against large rock that is on ground, much faster than hitting wedge with sledgehammer and wedge works better there. Of course there is a limit which I can squat, after 130 pounds it starts to get heavy, so need to choose which trees I make for 3ft and which I do smaller pieces directly.
Fiskars wedge costs a lot compared to cheap Chinese made ones, but it is nice steel, does not sent pieces of steel flying to your eyeball and it does not get stuck, also those logs it does not split completely are usually split easily with single hit with small axe.
Also rounded end works great as frozen pizza cheese breaker, damn cheese frozes solid, so that is my solution to problem