Easyclean, I have a stand off that bolts on and off after using the spring clip one from B+Q.
The disadvantage with the spring clip one was the depth it reached out from a wall. It was 12" I think and was inadequate for a lot of older houses where there is a deep overhang.
I actually took it back after about 10 uses and got a refund!
I ordered the bolt on from a website and it has a 17" - 24" stand off which is adjustable.
It is a pain with the bolts but takes 5 minutes to put on and is very secure.
There is a stand off called a Limpit which looks excellent but looks like it could be very pricey.
www.smithslimpit.co.uk