say where the presence of external test software shows up a fault in a router which is not harmful nor normally visible, it reduces user confidence unnecessarily
Sorry if Im being a bit slow, but I cant quite think what you're attempting to say. What type of hardware fault in the router would you mean.... or do you mean to say about line diagnostics. If you mean line data then Id have to agree with eric that the information available is "very helpful to a more knowledgeable user."
The danger is that some users get hooked and overly concerned about certain things that are within the realms of normality. The sad fact is that although this information can be very useful, there will be some who take it to the extreme. We've seen it happen many times before which has caused certain router manufacturers not making such information available anymore (eg Thomson/Speedtouch) and ISPs deliberately locking down routers.
Ive seen a document somewhere (cant recall now what it was exactly and where it was) but BT was citing DMTtool by name as a reason why there were problems when the EU's starting tweaking their SNRm and causing instability issues.
Its no big secret that it was the likes of BT that had the [purchasing] power to get Thomson to totally remove certain info from their routers.