I've been using them for almost two years and can comment the following:
Claims process is pretty cool - I had a windscreen replaced with absolutely no hassels.
I am paying an increased premium to have zero excess, so that is a possibility.
I used the excess funder option for cash back for a couple of months, sitting with about 18k in the account, then switched to proper cash back. The excess funder account can be used at TWT for tyre related purchases (not other things, I was told). It is also linked to your discovery drive status - the higher your status, the larger the percentage of purchase you can fund from it. If I understood correctly, you can fund 100% of your tyre purchase when on platinum level.
Driving style - I drive a bakkie, so that sort of eliminates harsh acceleration and braking, so only speeding and phone use to look after.
DQ Tracker - weirdest incident was driving on a dirt road on our way to the farm a couple of months ago. Drove through a pothole (or whatever you call them on dirt roads), got a call from discovery a few minutes later asking if everything was alright, as they got an alarm from my car.
Garage - remember if you use BP, you can also swipe your PnP card to earn their points.