I have one,
and I use it to plant corn, peas and, beans,
it planted radishes 3 seeds to a spot, and that was close enough at the time...
I test the seed plates inside on a carpet where I can pick up the seeds and try again to find the correct plate (if there is a correct one)
they have names for each of the plates, mostly ignore that, just look at size and spacing.
when it does work, it is fast,
there is nothing like planting 1/4 pound of corn seeds in 7 min.
even if it did take me a day to set up the ground to be able to use it,
i would have done most of that to the soil anyway.
if you care about precision, you are likely not going to like it,
it saves me enough time so that I don't care about the lack of accuracy,
what I am waiting for is a small seeder that uses a vacuum to pull each seed out (the best way to do it), but will likely have to build my own.