I thought that I might chirp in here.
After allot of reading and internet searching I thought that I had it nailed down to 2. the
Incra or the
Dubby systems.
But then my wife made my decision for me.
She got me a the Rockler miter sled for my birthday a few weeks back. I have to say that it has been the most accurate thing that I have ever used before.
I now use it to check the squareness of anything that I need to check or to make square.
I can't say anything about the others as I have not had the pleasure of using those.
It has a large sled base with integrated material hold down.
The fence moves easily to desired angle and locks in place by large knurled knobs.
the angle indicator has a nice sized magnified viewer (helps with the over 40 eyes

)
the Fence also comes with a material stop with flip up action.
The fence will also extend out in length to almost 26" I believe.
It was easy to square up to the table saw and start to use.
Be sure to tune up your table saw prior to squaring the miter to it.
It is large and will take up some space. But not overly big in my book.
the miter track that engages into the tables saws track comes with adjustable tension to take up any sloppiness that may be between the two.
I do allot of panel cutting for cabinets so I needed one that was sturdy, accurate, and big enough to handle cabinet side panels.
But I also wanted one to do small parts too. I think my wife found one for me
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.
She alos purchased the drop off section for it. making the system zero clearance.



Flaw

is if you have to put in any other size blade in your saw other than the one that you used to square the unit to your saw with. You will end up cutting the base sled shorter ie putting in a stacked dado blade.
You will no longer have a zero clearance, but for the dado.
Hope this helps.
SOme other had asked me to write something about this.