I just tried it - and it perfectly works

The current flymode is perfectly compatible with the old one (Esc to disable and enable, space bar to move up and down alternately), but in addition, you can use Num-Pad + and Num-Pad - to move down and up (as Chuckles said, "-" moves up as it is the upper key on most keyboards - all keyboards I know, actually).
Thanks a lot for the tip, D'Lanor! I think this solution is satisfactory for everyone, isn't it?