Marcus,
While the price point seems inexpensive (under £30) understand that it does NOT eliminate points (at least it doesn't look that way from their information) which is something that the well known and proven Pertronix does, or even the Crane XR700.
These have been talked about for many years. The Pertronix uses a Hall effect pickup inside the distributor activated by a magnet ring you place on the distributor shaft. The Crane uses a shutter wheel and an optical sensor. It's always been said that either of these devices won't make up for a worn distributor so best not to try and correct distributor problems with one; ensure your distributor is "up to snuff" as they say before fitting one.
Of course if you have some kind of ignition issues AND your distributor is worn that 123 distributor replacement seems to be the universal choice.