Possibly too much sun on the parsley. If it's hot, I'd make sure it has shade from noon onwards. Same with the coriander.
Don't know what to say about the slow growth. Looks like insect damage on the basil.

I'm wondering about the choice of potting mix. I looked at the website and saw nothing that indicated that their products should be used as a potting medium. Does it drain rapidly when you drench the pot? The crispy edges can be an indication of a moisture problem.....excess or insufficient.

The little spots look like early thrip damage. I see it on the parsley, too. They've probably invaded the cilantro, too. :-(

Those are very big pots for the size of your plants. They are busy growing roots.

Is this a thrip on my basil??

I only found one. I squished him and pulled of the leave. What should I do further?

The leaves..

Also after last night my cilantro seems to now be trodden on/broken and sticky stuff remains over the mix and the stems. I suspect snails since we have a lot of them in the front yard (and maybe the back then). Should I trim off what is damaged and put down the snail killer I used in the front yard (to good effect) - we have no pets or kids (well none that frequent our back yard).

Yes, that's a thrip. On such small plants, I'd say it'd be easiest to just keep squishing them when you find them, but there are organic applications you can use to discourage them as well. They'll have nothing to do with the growth rate.

Zzackey is probably right; the pot size could well be the problem. They're likely spending a lot of their energy growing roots. It also means that the soil will stay wet for a long time: in the ground the moisture drains away freely, but potted soil relies on the plant's roots to soak it up. There aren't going to be enough roots on such small plants to soak up all the moisture. The leaves are probably showing signs of oxygen deprivation as a result.

Uh oh. Not thrips at all. Instead, a leafhopper. (Thrips are much smaller.) And the white spots are from leafhoppers. (Thrips damage is quite different.)

That certainly looks like snail damage on the Cilantro.