One of the problems of using a grinder without a hopper for single dosing are the jumping beans. You can put a tamper or cover on top to keep the beans inside. But the grind results are different from grinding with a filled hopper, you have to grind finer to get the same extraction. And I believe the grind results are better with the pressure of a filled hopper.
There are grinders built for single dosing, like the Kafateks, Lyn Webber EG-1 and HG-1, Malwani Livi, and others. They all have some kind of cover to keep the beans from jumping out. Now my question: would these grinders perform even better when they would have a column of beans on top of the burrs, pushing the beans in the right direction?