This guy's channel is great. He has some land out in the wilderness and on a series of extended vacations built a pretty decent log cabin and bunch of furniture and craft items, basically all by hand with self-made tools (less the chainsaws, obviously).
That's exactly where I learned to do the free hand milling technique. I'm still using a cross cut chain (I ordered a couple ripping chains from granberg tonight) so my slabs aren't as pretty as those, but they're pretty uniform. I'll grab a picture tomorrow.
For my pine slabs/posts I use a tape measure to locate the edge of a full 4x4 post on the log and drive a 3" screw about an inch into the log. Then I hook my chalk line over the screw and walk to the other end, locate the edge of the 4x4 post on that end, and snap the line. Finally, I roll the chalk line back up and remove the screw. I initially make a shallow first pass that goes over the chalk line then make progressively deeper passes using only the tip of the bar and paying careful attention to my form and maintaining the bar perpendicular to the ground. For a 7 ft long 25" diameter log it takes me about 10 minutes (I haven't actually timed it but it feels longer than 5 and shorter than 15) to get all the way through. Of course this is 3 minutes of cutting and 7 minutes of me shaking my arms, groaning, and generally wondering if a fence is actually necessary or important. My first slabs I had the log on the ground and kept dipping my chain in the [very sandy] dirt, instantly and frustratingly dulling it. I eventually wised up and started using a thick slab as a cutting bench so I can plunge without worry of getting the chain in the dirt.
Free hand milling isn't be too bad for making slabs, but I'm looking to make a few dozen fence posts for the perimeter of a 5 acre property. That makes setting up what is essentially a jig for milling (chainsaw mill/sled) worth the effort to me. I'm sure I could eventually get on his level where I could mill for longer than 5-10 minute stretches, but I'm trying to finish milling these fence posts sometime this year!
Edit: I forgot to mention that the shavings produced using this technique are super long, way different than cross cutting. A couple of times I've been very close to fully separating a slab from the log and started using more than the tip of the bar and packed the saw so full of long shavings that it jammed. I've got a Stihl MS261 (coincidentally I think the same saw he had in that video) which is a 50cc engine. I've been saving up some new tool money for a few months now and may end up getting an 80cc saw for milling. Before I pull the trigger I want to spend more time milling and woodworking in general.
Edit2: I'm watching the video again to refresh my memory. He does mention the long shavings, and then he talks about using bungee cord as a guide. I initially tried using masonry string and after cutting it a couple times decided to switch to a chalk line. I've practiced enough now that I might be able to use the string again, but it's not obvious to me that the string would be any quicker than marking with a chalk line.