Kep - no problems on the 12". The main points are 1) make sure nothing overhead or upslope is going to come loose, 2) have a trip-free escape path to back away if things go sour, 3) know that you are a major hazard to any 2 or 4 footed onlookers, 4) pay attention to bind and know what the different ones indicate, 5) pay attention to cracking noises (no ear muffs) and what they indicate, 6) plan the angles to make it easy to separate the lengths, 7) take long strokes, 8) keep your shoulder in line with the length of the saw blade.
All the sawdust must be cleared from the kerf on each stroke. Otherwise the sawdust builds up in the kerf, getting between the teeth and the intact wood, and creates extra friction. Of course you can ignore this and just put up with the extra work. Also in this regard, the fine teeth on Fiskars doesn't drop wet or gummy sawdust. If you have a lot of this to cut, there is
the 21" Corona 7160 D-handled pull saw for $45 on Amazon with no sheath. Its a nice saw. It clears better. But the teeth are too coarse for 1.5" diam and smaller, thus requiring another tool/saw to fill the gap between the capacities of a pair of by-pass pruners and the Corona.
For the 18" Fiskars on anything over 8" dia, first use an axe or hatchet to cut flat faces on the front and back side. The cross section will look like a 1/4 mi running track. For example, chopping off 2" on either side of a 12" log will reduce the kerf length to 8". It doesn't take very much effort to chop off a couple inches on each side. The practical limit is something like 18" dia. There are other techniques, like cutting 1/3 the diameter, rotating the log 90 degrees, cutting another 1/3, and so on, but this results in kerf that is not flat on the sides, and this causes the saw to bind.
That said, when I have one of my crosscuts with me, I'll use it on everything 6-8" and up because it cuts on both the push and pull, allows a much longer body stroke, and I can stand that much further away from the cut on the final few strokes.
Ok, I'm guessing that's definitely tldr.
