I have the Thule roof system and it works well. As mentioned above you do need to take care lifting the bikes on to the roof but it's not a great problem. My car has a sunroof and I did need to take care positioning the bars to make sure they didn't foul the sunroof as it retracted, but there was just room to do that. You would be best to open the sunroof and then position the bars so that you can see how close you can get them to the sunroof without catching.
We now have a couple of electric bikes which are each just over 20kg. The bike shop did tell me they have seen people using roof racks with them but I didn't like the idea of either lifting them up to the roof or having so much weight on the roof, although technically it would be within the limits, so we bought a towbar mounted version as we already had a towbar on the car. It was expensive, about £500, but works very well.
We now have a couple of electric bikes which are each just over 20kg. The bike shop did tell me they have seen people using roof racks with them but I didn't like the idea of either lifting them up to the roof or having so much weight on the roof, although technically it would be within the limits, so we bought a towbar mounted version as we already had a towbar on the car. It was expensive, about £500, but works very well.