Hi Pete,
Tried it years ago (ESP anchor rig tube) and didn't like it at all. Use it all the time on stillwaters but in a river it's pants! It's also difficult to keep your rig in place due to the force of the water on your rig.
My main reason for trying it was to see if the fish would or would not recognise it as tackle in clear water and thereby hiding your line. On that front it was successful to a point but they soon sussed it out as being tackle in the swim.
I have since messed about with various things such as leadcore and backleads, long hooklinks etc but nothing has made any descernable difference as far as i'm concerned.
I made one rig which consisted of various bits includong leadcore and backleads and reconned that, if for any reason, i got snapped up, it would cost me over a fiver to re-tackle!
Hope that is of some help.
regards,
Jeff