slotted can be machined.but, alot of places wont.
can damage the teeth if cut too deep, if cut shallow, can take too long and they dont get their monies worth/profit.
I initially went 1000s because years ago when I got them, I wanted pkug n pkay, and they were much cheaper then 2000s.also, e85 was no where near readily available.
will be getting some next stage though.