To me it seems like if you only need a few to be successful then doing it manually will be just as effective (since you're doing it manually, your success rate will be much higher).

In either case, it doesn't bode well for this startup's claimed goal. I'm sure their bank account on the other hand will be fine though.

it's probably cheaper/easier to send drones with lots of seeds over miles of land rather than workers with a few seeds

Workers don't plant seeds, they plant seedlings (that are 2-4 years old, depending on species). You get a much higher survival rate that way. It's costly, but so far it's the most efficient way. Maybe drones will change that eventually, but I doubt it'll do it by firing seeds.

You can probably take a drone with a load of seeds much easier to remote areas than shipping large numbers of few year old trees.

Areas that are too remote aren't typically the ones that get deforested though - generally trees are removed either because they're valuable (and if you can bring trees out, you can bring seedlings in) or because the land is wanted (which usually means it's accessible).

It's neat technology, and I hope they succeed, I just worry it's a cheap way to say "we're planting thousands of trees" while doing very little of value.