The Tremol-no is a device which , when installed in a guitar with a floating tremelo system, can be used to either prevent the tremelo form rising out of the guitar's body, effectively making it a "dive only" tremelo(reducing the risk of string breakage, or it can be used to lock the tremelo down completely, as if the guitar had a fixed bridge. This can be done by fastening the screws on the tremol-no.
The tremo-no is an invaluable piece of equipment for the guitarist who needs to alter the tuning of a guitar, who would in any other case not be able to because of it's floating tremelo system.
I use the tremel-no to change between standard and dropped tunings on my guitar which has a "Floyd-Rose" tremelo system. Without the tremol-no, this wouldn't be possible.
If I were to have a small qualm about the Tremol-no, it would be that in order to fasten the screws which either fix or limit the tremelo's ability to move freely, excessive force is required to ensure it is absoloutley tight.
In conclusion, the All-parts "Tremol-no" is a useful piece of equipment for the guitarist who has a guitar and needs it to do everything - at once capable of string snapping dive bombs and vibrato, the tremol-no will fix the bridge of the same guitar making it perfectly versatile.