Had them on for prob around 30k. Mix of motorway, but last 10k local really with some harsh braking....

When the car has been stationery overnight I can hear a grinding type noise when I apply them..

could just be rust my rears have rusted a little on the round the edge which is starting to cause some noise

How long is a bit of string? It all depends on the car, the type of driving and the conditions, the only way you get to find out is by having a look.

I remember reading somewhere today at work, not sure if it was on an invoice or sales brochure from a part supplier but...

It said they are suitable for 25,000.

Edit: it's possible the info was on pagid brakes also... In my opinion Mintex are a soft brake pad so might not last as long.