One Credit per Child ASIN (Variation)
Depending on your current plan, you will have a certain amount of credits available - in the trial phase that means 50 credits. You would therefore be able to track 50 Child ASINs during your trial.
Whenever you add a product with multiple variations (Child ASINs), it will automatically add all variations to the monitoring. This is why you would, for example, not be able to add a product with 51 variations during the trial.
Number of Variations in Right Column
The number of variations for each product can be viewed in the respective column of the Spy overview:
Unfortunately the tool has to be limitied in this way as the "crawling" of this information causes the largest effort for the system. Currently it is not possible to monitor single variations.
Once a product is deleted from the monitoring, its credit(s) will become available again immediately.