It's pretty good by all accounts. I almost joined the pre-release months ago, but it would have been around 6 months before receiving it, so I have waited. I bought a second V400 for $500 USD Brand new, which is absolutely insanely low price. I would like the S1 for sure, but I am skeptical of any real improvement in SPEED for PETG since it needs time to bond/lay. I would gladly be proven wrong though.
I like the integrated dryer and enclosure. I also like the hefty weight of it. Even my V400 moves around a little and that's a bit of a beast already.
My only bug bear is that delta's can't do multi material that I've seen. (Without a lot of wastage).
If the S1 were to bring a significant improvement in quality over the V400, I would absolutely consider it. i.e. accuracy, better and easier calibration etc.