Peter
My two soil block trials are now sufficiently advanced that I can say with certainty that they are very good for germinating Sweetcorn seeds (32/32 within 2 weeks although some are further advanced than others) and for Scallions (using Ishikura seed from QuickCrop), where germination is transformed compared to the rubbish I have had using White Lisbon seeds from large manufacturers and huge numbers of seeds have visibly germinated within 7 days.
As I wish to keep the Sweetcorn in the blocks for 4 weeks, time will tell if the plants are happy with that. I suspect by the time the Scallions are ready to go into the garden, things should have warmed up sufficiently for this not to be a problem.