I got this when i was first trying to learn to abseil.
it's well scratched but hasnt actually had that much use, it kind of works like a stop, but it locks if you let go of the handle or squeeze it right in, to move you have to find the sweet spot in the middle.
It's awesome to build up confidance, and has rigging diagram on both sides (for left and right handed people) but i wouldn't recomend it for a big technical multi pitch trip.
some blerb from here -
www.safelincs.co.uk/anthron-self-braking...Li47UCFUvHtAodWGIAoA
The Anthron DSD 30 self braking descender features an anti-panic function which allows a safe descent when the correct pressure is applied, but will halt the descent if too little or too much pressure is applied. This protects the user if they panic and squeeze too hard or completely let go of the device.
•Anodised aluminium construction
•Built-in anti-panic function
•Suitable for use as part of an evacuation kit
•Conforming to EN 341 Class A and EN 12841 Class B
•CE marked
theres one on ebay at £50 and a new one at £110
i dont think they are worth that, so £25 and it's yours.