I use a related setup when milling with my small milling rig.
Being able to leave the mill and saw on rails makes it much easier to start and finish a cut is one advantage, and not having to lift the mill and saw on and off the log for every cut is another
Some of the disadvantages I have experienced with this setup are
1) Having to adjust the height of the bar relative to the log for every cut is a bit of pain. I have cranks on my uprights on all my mills which enables me to hold and make relatively quick fine adjustments but I still find it a nuisance.
2) Threading the saw on and off the guide rails is a real PITA.
This is less of a problem for small logs where multiple cuts can be made on one tank of gas and one chain touch up. It is a problem for saws (like the 076) that have the mix tank on top of the saw (ie on the front side when in the milling position) and, unless an operator is able to sharpen with the bar in the milling position, the saw and mill have to be removed from the guide rails. This does not matter if you remove your saw from your mill to sharpen anyway.
I have used a long clamp that clamps the bar (still attached to the saw and mill) to the top of log so the log rails can be threaded through the mill. This works OK on a big log, but is more mucking around and only works on little logs of they are clamped down into place.
Another approach is to make the log rails wider than the mill uprights and use mill rails that overhang the log rails. This enables the mill to be threaded up between the log rails. However this also means either, i) placing the inboard clamp even further away from the powerhead losing valuable cutting length or ii) operating the mill at extended heights so the mill rails overhand the saw at the inboard end. It's still a clumsy method
3) Cannot as easily place the logs on a slope to mill.
Although one can orient the whole frame on any natural terrain slope, sometimes there is none available and creating one artificially is much harder with this type of setup
This is for me the main reason why I still have not gone for a carriage mill. Although one could add a winch
4) length limitations.
I prefer not to cut the log length to suit any logging frame although scaffold has the advantage of being able to set 2 frame lengths if one needed to, but that make even more stuff to carry around and into a milling site.
If you are happy to work within those limitations then I agree it is a handy setup.
