I will be in Germany for one month and want to purchase a D-ticket. I have two apps on my phone hvv switch and mvv-App. These seem to be the easiest ones to use as they do not require a local address etc. I would appreciate suggestions on which one to use. I have looked at others, but not to excited about using them. Thanks in advance for your replies.
Of these two, HVV switch is the simpler option for my taste, because you don't have to set up a separate account and buy a ticket. Don't forget that you have to cancel before the 10th of the month so that the ticket is not automatically renewed. There are a few resellers who illegally circumvent this binding rule, e.g. tranzer.com (with a markup of a few euros), mo.pla, or Autobus Oberbayern (the operator of the Lufthansa buses; check the "single ticket only" box); but as long as the DT Agency lets them do that, you don't need to worry about it. The Man in Seat 61 may know of others.
I used this last September: https://ticket-direct.themobilitybox.com/en/orders/new?fastlink_referrer=b4f5cc&product_id=mobilitybox-product-9e82a4eb-0cc5-4a07-b629-cf2b9ea8fa56 There's a dropdown option (Subscription Mode) that cancelled the subscription immediately after purchase, so I didn't have to worry about remembering to cancel it in time.
I was able to save the ticket to my wallet on my phone.