I am not sure if there is an English version of this page. If not, pls use Google Translate.
"Get the sample BahnCard 25 by July 18, 2021 at the unbeatable price of 9.90 euros. With the Probe BahnCard 25 you save 25 percent on the flex price and the saver prices in national long-distance transport for three months."
The regular Bahn Card page also offers trial cards, in English.
https://www.bahn.com/en/offers/bahncard
It should be easy to get value at that price. In 2019 I paid €19.90 for my (trial) BahnCard and it paid for itself after just 3 tickets. At €9.90 it would have nearly paid for itself with just the purchase of the ticket for my longest train ride.
Make sure you read this (from the FAQ for the BahnCard) before committing to a BahnCard.
You can cancel your card in writing up to 6 weeks before it is due to expire. If you do not cancel
your card, it automatically becomes an annual subscription.
Make sure you understand the cost of an annual subscription and where to write to cancel before committing. Unless you are going to be going to Germany often, you probably don't want a BahnCard subscription.
