I am very much looking forward receiving the O-GPS1. But German customs is very slow. To make the customs check easier and faster it is very important, that you give a value/price on the parcel. You could include an invoice on the the outside, which the customs officer may see and check. Whether this invoice is to the real price or believeably lower (lets say 35 USD or so), is up to you.
税関検査を簡潔に早くさせるには、小包に価値/価格を記載することが重要です。外側に請求書を貼るつけることもできます。それを税関の職員が見て検査することができます。この請求書が実際の価格かそれより低いと思われる金額にするか(35ドルかそこら)は、あなたがお決めくださって結構です。