The address book plugin is designed decently and it is simple to use.

Never try to send a single message after selecting an address book group - this will result in sending the text message to the whole address book group.

~0.10 EUR / message is quite fair, especially for international text messages. The additional annual fee of 10 EUR is in my opinion a bit of a rip-off, though.

Almost every text message reaches its addressee - otherwise you will be informed by email and your money is refunded.