A reeler on a plough saves a lot off effort. A reeler on a plough gets in the way wherever it is.
It also affects the weight distribution. They need to be able to turn very easily even on a side slope.
You can mount as many as say, 4 reels on a machine, but even then there will be cases where you need to bury more and you will have to lay some out on the surface. 2 reels is a good number because they can be mounted side by side and you may get a bit of vision between them.
With a normal farm tractor the reelers are liable to be somewhere at the back, because a tractor is designed to attach things there and it is close to the feeder tube to the plough. With a purpose built plough the reels can be at the front which is useful as a counterbalance because the plough attachment is very heavy. As for getting in the way , at the back it hinders the volunteer getting duct off the drum, and with being able to see the ploughblade and to access it. At the front or back hinders the view of the driver.
You would normally need some slack in the duct to be maintained by a volunteer rather than expecting the drum to self-feed.
This one from Chipping B4RN is the best one to date. It manages to give excellent visibility.
Not sure if it could have coped with the larger drum that was being used at one time. And if that feeder ring wasn't a complete ring then it would give you the option to un-feed it easily in cases where a volunteer needed to help put some slack in the duct. And it has no removable back-plate. But this appears to have the basis for a perfect set-up.
This one makes it difficult for a volunteer to keep some slack in the duct.
This enables a volunteer or two to access the duct and be able to assist with turning the drums, whilst maintaining good access to the plough and good vision. The driver and the people at the back have lost contact though - it can be noisy and hand signals are useful.
This 3-reeler version is designed to work best as a self feeder. It is very difficult to assist with turning the drums and also to access the plough.
It will be very difficult to fight with 4 drums especially ones close together that will have trouble turning independently. And a second person has nowhere to be.
This works very well for the people at the back of the plough. And on this type of machine the driver has excellent visibility. Slightly restricted view at the front means a spotter walking ahead can be useful.
Sometimes a machine will self-feed. But often tension needs to be taken out of the ducts
Adding a slope to the proceedings will make things more difficult as friction increases
There's a lot here that is going to need further design. A lot more rigidity and a big lot of mass are needed for the plough. It appears to have potential to reel from about 8 drums - which would have to be attempted at some point, but only for fun.
You could just use it for transportation, if you have some general direction that say your core route is following, then you have moved all your stocks to where you need trhem.