Anyone in Germany buying bitcoin for the first time downloads an app and almost always pays more than they think. The visible part of the cost is usually small or absent altogether, because many providers advertise fee-free trading. The real price sits in the spread, and across the five apps in this comparison it ranges from 0.15 percent to 2.49 percent per purchase. On 100 euros that is 15 cents or 2.49 euros, and over a year of savings-plan instalments it becomes a difference of several dozen euros.

The second question matters even more for beginners and is asked less often: who owns the coins after the purchase, and can you get at them at all? An app that does not permit a transfer to your own wallet is selling you exposure to a…