I became concerned about using these as there were reports of them being recalled by BT as dangewrous!
Details on the internet are now sparse and have been removed from BT.com . Having scoured the net it appears that the Model affected was the Comtrend DH10PF where the case could become brittle with use. It was then possible for it to break and expose live wires.
BT seems to have replaced all of the DH10PF for which they had customer records. However, an official recall for the product was not issued as BT appears to have been the only "supplier".
There are many of these for sale on Ebay, so I advise that you give them a miss and buy a later model,