This year and last year I used New Horizons peat free. I have sown parsnips, leeks, carrots, salsify, french beans, chillis, beetroot, pak choi, spring onions, sweetcorn, root parsley, courgettes and winter squash. I have had very high germination, which I put down to quality seed. My leeks are a bit slow, but other plants are fine. The pak choi has been big enough to eat for a week or so. I also have Aldi peat free compost, the french beans like it. The NH varied, one batch was lovely and fine, the next had a pine resin smell, and lots of fine woody bits. The Aldi was finer, with a few twigs. As far as I can tell it's all very usable. A few twigs do no harm. Yes there are small bits of plastic in the NH, obviously shredded plant labels etc. I've also used my own compost, but it was a bit too light, due to spent hops which had not fully broken down.
Frankly compost is compost. Seeds use there own reserves at first, then need some fertiliser from the compost. Then you feed. The only failure I've had is potting up three self sown lupins, two died. I think the compost was not water retentive enough. The next two potted up were dug out with a decent clod of clay soil around the roots. Was this the fault of the compost, or me?