I've just ordered a 2018 Octavia from Cazoo for delivery next week. So far, the process has been a breeze (just like the adverts!). Also their customer service has been excellent. I've called them up several times with specific questions, to which they've replied via email by end of day. It's due its first MOT in May and because that's within 6 months they will include that for me. Paying first before test driving it is a backwards approach, but I am reassured by their 7-Day Money Back Guarantee and my credit card's payment protection (some dealerships don't take credit card). I did ask if they can deliver two cars(!) so that I could pick between manual and automatic but unfortunately I'd either need to outright buy them both, or return the first one.
Personally I wouldn't do this with older vehicles, or an independent dealer, without some degree of trust. However I have no problem doing this with a large car supermarket.