I use the mix with fine sand trick. One caution if you're seeding outdoors -- DON'T TOSS your sand/seed-mix ....
... they separate remarkably well mid-air
. Drop a pinch every couple of inches (carrots) or 3~4" (lettuce) where you want the seeds to go. Since both lettuce and carrots should only be lightly covered, if at all, I "dust" the fine sand mixed with compost over the entire area afterwards.
I admit I started carrots seeds ahead last year for a long maturing type called Healthmaster (110 days). It worked well albeit a bit tedious to handle carefully. But this year, I've been way too overwhelmed with other seed starting projects, so I just direct seeded. I HAVE re-located a few seedlings outside when they were growing in the "wrong" place. They seem to be OK being moved around as long as you water them in well.