I don't know if any still exist but I remember when I was a teenager in Liverpool I used to see a gentleman nearly every day riding an ancient push bike with a tiny engine fitted to the front forks, it appeared to work on a friction system. It was a noisy thing but in those days we didn't worry about things like that.
So bloody dangerous.... some of them have a nice little flag they stick up to let you know they are there. Strangely enough, the height (and therefore danger) was one of the main reasons why the C5 bombed so badly. Maybe it will make a comeback... but only if it gets a roof!
Caveats apply as it is entirely possible that the information contained in the above post is either an attempt at a wind-up, an attempt at a joke or just plain wrong.
Oh dear - I've been caught out. Actually I didn't have a clue. All I did was to google 'recumbent bikes' and browse the first non-wikki entry to see what piccies they had. I've just repeated the process and discovered it's a conversion job using a kit supplied by Cruzbike.
The kit is fully reversible, so it can be removed to return the recumbent bike to back to the original mountain bike, or used on another frame if you want to try something else.
So long as the motive force is set ahead of the wheels it should be okay as I'd imagine that driving a wheel set ahead of you and your feet would be much more difficult than the usual set up. Even those shown that drive the front wheel have the pedals and feet set ahead of the wheel. There may be some other factors in handling but not to the extent it effects cars and their drives.
Hope is but the first step upon the road to disappointment.