Microgreens for the windowsill

Anyone else growing or grown microgreens? We've been trying radish, broccoli and sunflower, growing them in those 8x13.5 inch trays which fit those flimsy 24-cell modules. The growing medium is just old pepper/tomato potting mix, sifted. I've used the same stuff 4 times now, just taking out most of the roots and levelling the surface before re-sowing. Radish and broccoli are incredibly easy, sunflowers a bit more finnicky. I just scatter the seed fairly evenly over the surface of the medium then put a tray over the top to block out light until they germinate, at which point they go on a window sill and are ready for harvest in a couple of days. 

Using the recommendations of this calculator - https://jscalc.io/calc/vqHxgaGIt3RncroW - per tray we're using 20g of radish/broccoli seed and 50g of sunflower seed. We're yielding 150-200g per tray. The seeds are from Premier Seeds Direct and it's working out at 40p/tray of radish, 55p/tray of broccoli and 67p/tray of sunflower. Buying the seed in larger packs would bring the price down by 10p or more per tray. I'm not exactly sure how much fresh microgreens sell for online, but it's got to be significantly more than £2 - £3.35 per kilo!

They're a good addition to salads, very nutritious, grow incredibly quickly and it doesn't matter about low light levels during winter because even though the seedlings get leggy, the stems are still very tender.