In the Mycroft 2018 review the top 20 skills by number of invocation are listed. There is also a spreadsheet with all skills attached to the review where the fhem-skill is #42 of all ranked skills. I think that is not too bad considering that the fhem-skill was first published in second half of 2018 and the FHEM user base is rather low in the Mycroft community (comparing to other home automation systems like Homeassistant or OpenHab).
Thank you all for using my skill - I think its about time to move to the Mycroft Market now…