If you are business seller do not use them. Many undelivered parcels while tracking number shows they've been delivered. It takes couple days for customer service to reply to your e-mails and usually they cannot resolve your problem. They ignore your questions or do not reply at all.
We are using their service after switching from other German address provider and I am delighted that we did it. They are always helpful and responding to all our queries very quick. On top of that prices are very good. Definitely recommend this service.