There were two issues of the 1 Groschen stamp. The first ,as already mentioned, is Michel #4, issued Jan 1 1868 rouletted 8½ -11½. The second issue was in Jan 1869, Michel #16, & is perf. 13¾:14¼. Michel states that both issues have shades & both catalogue @ 2 euros used.
Michel #4 is available imperf & is catalogued @ 150 euros mint, no mention of used but a note that you're going to need serious margins to prove that it's really imperf & not just cut down.
In any case it's not an imperf #4 you've got but a cutout from a pre-printed envelope that came out at the same time. I've blown your pic up to show more clearly the two diagonal lines of overprints in grey which run across the indica. they read EIN GROSCHEN POST - COUVERT. Quite easy to overlook if you don't know they're there. My ancient Michel Postal Stationery catalogue has the envelope @25 marks used, so I don't think the cutout is worth much, I'm afraid.
