Very interesting post Tomáš. Why did you choose GraphHopper instead of BRouter? For me offline BR with Locus has the advantage I can (with support from clever people) modify the selected fastbike.brf profile to suit local conditions (eg. cycling allowed on motorway, add more cost to gravel track) whereas with offline GH with Locus the rules & costs are not modifyable by an "ordinary" user, and there is no script customization possible. The script ability of BR has made its routing choices near to perfect.