if you do a search for "futz" or "hansenfutz" you'll find various threads.
I was interested in those pedals myself (for some time). What I remember from some of those threads is that they're far better than nothing but feel noticeably different than a real pedal as they create a unidirectional resistance when operated. Also, the overall design isn't too sturdy (with some parts being prone to break off), and one should try not to overtight the setting screws to keep the threads intact. Best check them out so you'll know whether you like it.
I've done a short search, here's some threads I found: