I've been using Verve from B&Q this year, and it's been ok. There was a spilled bag from the pallet from which I took my first lot, and that looked good, so I felt safe. I'm sieving it for seed sowing, as it does have some bitty bits in it, but having sown into fifty 3" pots this afternoon, after sieving, I had less than one 6" shallow pot of 'rubbish', which will be fine after time in my compost bin.
I've used it for all my seed sowing as well as big flower pots. All the flowers are doing well, and apart from Orange Winner marigolds, which I've decided was a duff packet, all the seeds have done well.
I've also used in it my half-barrels for peas and beans and the peas are doing very well. The beans are suffering from the weather and being almost drowned, so I can't blame the compost for that.
Miracle Gro, on the other hand, was a disaster for me two season ago, and I had to begin again from scratch after non-germination of almost 90% of sowing.