As for the cost ! It adds pence to a run when using oval conduit .
If installed correctly , it is perfectly accessible when it comes to replacing , even pulling the odd extra cable down when needed .
It looks 100% more professional to the client than just clipping direct , no matter how neat your clipping is , and a damn site quicker .
The above does depend on if the chase has been cut with a decent wall chaser ( but then again if you have not got this or the extract gear to go with it , I pity any other trades working along side you on a rewire ! ) .
I know it is purely down to choice , but it is a no brainer as I see it .