My husband made one like Burra's picture. He made it out of PVC. I am the one who used it and found it very helpful and easy. No bending over so it was easy on the back. He had dug the trench and went behind me to cover the seeds.
Invasive plants are Earth's way of insisting we notice her medicines. Stephen Herrod Buhner
Everyone learns what works by learning what doesn't work. Stephen Herrod Buhner
I am using some of them to plant Garlic and Saffron because everybody believe that Garlic must be planted heads up.
At least here ( Italy) there are several of them manufactured locally, with holes ranging from 20 mm to 60 mm
If I can make a suggestion:
Purchase the big ones.
Than it's easy to insert a smaller pvc pipes in order to deal with the small plant / corms