This isn't really going to be a fair review as I have only used a handful of different silky's, but that is mostly because once I used the Natanoko I knew there was no point in trying anything else, it is a monster.
It cuts quickly and effortlessly, its wide set teeth are perfect for larger diameter branches both dead and alive. The long sightly curved blade means you remove a lot of material for every stroke, making cuts quicker and easier. The blade has a nice rigidity to it meaning when cutting at awkward angles it maintains its angle of cut, something cheeper saws struggle to do.
Now I'm sure other Silky saws do all of these things, but for some reason I have never got on with them, I either find them too small, to curved or too flexible.
As for other makes, well I personally wouldn't bother, they are generally cheaper for a reason. Buy cheap buy twice. I used to have a samurai brand one and the scabbard broke within a few weeks and the blade dulled very quickly. I've also used the CEUK ones and they are no better, very flexible blades that struggle to cut in a straight line and just make it look hard work.
There are only a few faults that I can think of, Its not the best for very small diameter stuff as the teeth are fairly aggressive and it can if your not careful leave a ragged cut or tear the bark. But if I'm doing a small reduction with lots of small diameter branches I almost always have my Felcos on me anyway.
The second flaw is with the scabbard, the hole at the bottom is not really big enough and sawdust does tend to accumulate occasionally leading to it blocking and preventing the saw from seating properly. Although this is easily fixed with a stanley knife
I also found i didn't really like the way it hung from my harness, it was always at the wrong angle or twisting itself round making it tricky to return the saw, especially if cutting and holding.
This was easily fixed by removing the clip that came with it, and replacing with some 6mm accessory cord, a small wire gate wild country biner and a Karabiner retention rubber
This keeps everything low profile, no knots as its held in place by friction, and the alinement of the karabiner means that when clipped into my gear loop the scabbard is flush with my leg
Only a little thing, but when you think how many times you have to get your silky out in a day it makes a huge difference if its always in the right place facing the right way