Okay time for an update.
I've had the Seasucker rack for some time and it's simply taken an eternity for my new MTB to come in so I had an opportunity to try it out. I had ordered a kit from Seasucker that included the rack, the fork spacers for boost space forks (the rack comes with an adjustable fork lock but I wanted an exact fit) and the kit threw in a free cable lock with a special device that fits into the groove in the vehicle trunk to secure it... not sure if that fits the Model 3... but hey, free lock if I ever need it.
Finally the bike (2019 Ripley V4) arrived and I got to use the rack!
First off, I did not crack my glass using this rack although I've only transported it a few times.
Secondly I am following Seasuckers updated recommendations for the Model 3 that has you placing the front suction cups on the rear glass and the back suction cup on the trunk deck lid.
This arrangement does make loading the rack a little easier, but more on that below.
I used some distilled water to wet the suction cups and had no issues with any damage or marks on my ceramic coated paint. The glass did not suffer any damage as previously mentioned.
Loading and unloading this rack is not hard, but I think the time when there is the biggest opportunity for glass damage is when putting the fork onto the rack or taking the bike off of the rack. It is quite easy for the fork to slip and it could easily hit the glass and chip or crack it. For this reason I strongly recommend attaching the rack to the bike fork and THEN placing the entire thing on the car.
The rack handled moderate speeds fine but, conscious of the fact that I was transporting a mountain bike that costs as much as a used Honda I did not do any speed/acceleration tests. I drove a little more sedately than normal. I could see that changing as I got more use and experience with the rack. Other reviewers have reported that they drive up to 80mph and accelerate and corner normally with their bike attached with suction cups.
Setting the rack up takes a bit more time than having a roof rack already on the car with a fork mount already on it. It took me about 10 minutes to get the bike on the car the first time and 5 mins the second time.
This rack seems to be an excellent low cost option for those who will only transport their bikes occasionally. If you transport your bike frequently then the permanent rack will probably be more convenient and offer more security.
All in all I give this rack five stars. It does exactly what the manufacturer claims, and it was reasonably priced at about $350 shipped to my door.