I purchased this chain lock to use as a secondary lock to my mini d-lock for securing my bike at work. At the time it was just £38 but has gone up since then. For my purposes, its great but it does have its limits.
At 4.3Kg its a heavy beast (excuse the pun), I wouldn't want to be carrying this lock around with me. However, if you'd feel comfortable leaving it locked in one place all the time (as I do) then the weight isn't a big issue.
The pad lock feels quite light and I wouldn't like to put money on it surviving a hammer attack, so always ensure that the chain is used in such a way that the lock can't be placed against the ground or a wall.
At 12mm the chain's links are not impossible to bolt crop by hand (you'd need upwards of 16mm for that) but combined with a second lock, preferably of a different type (i.e. a d-lock), I'd reckon that most bike thieves would move on, looking for an easier target.