Exactly how small is the pot? I assume it is not glazed? As long as you make sure the mix in it doesn't dry out it should be OK unless it is so small that drying out quickly is inevitable.
I don't know what might be in the compost amender, I looked it up and saw one that had stuff in it that I wouldn't use for a baby seedling. The vermiculite will be fine for the first month or so which gives some time to figure out what to do and to get the seedling to the point where it needs some fertilizer.
Here is a picture of seedlings that were started in vermiculite only and grew in it, no fertilizer, for a month just to show that "Tester" should be fine in just that.
