Here is the explanation of the subscription payment method-
1. Subscriptions can be combined
2. Should you decide to pay for the 2.99 USD / 2.49 EUR - 5 Gems per day subscription - you will be receiving 5 Gems per day forever. The 2.99 sum is paid just once, no need to pay it weekly/monthly - just 2.99 USD / 2.49 EUR once and that's it - 5 gems per day for life.
3. the 4.99 USD subscription will expire after 30 days - it will not be renewed automatically. In case you would like to keep this subscription, you will need to renew it manually every month.
4. If you are not able to log into the Trainstation game every day to collect your daily Gem reward from the purchased subscription – The 30 day offer will be prolonged. So if you do not log in two days, you will get two more days to it, so you will still be able to get all the Gems from this Subscription.
The Daily gems however need to be collected daily, and are not automatically added.