I've been testing Sulvo site-wide, in addition to my Adsense banners. Their system focuses on a single sticky banner, and you can choose where to affix it to your page. I chose to stick a 300x250 in the bottom right of my page, on all devices except for mobile.
This is actually working out extremely well for me! Yesterday, this one banner raised just under the same amount of revenue that 3 banners raised with Adsense! It started out raising about 1/4th the amount of Adsense, but since it was in-addition-to Adsense it was still just free money. But since then it has grown daily.
I had a few complaints from users that it was too intrusive, but after reviewing screenshots I honestly couldn't see why; the banner didn't hide any pertinent content. So I think they were just opposed to any change. I've kept an eye on traffic and pageviews, and traffic has actually gone up slightly, so no one left the site because of it.
I've also been keeping an eye on Adsense, and nothing has decreased... the click through rate is still the same, and the Page RPM hasn't really changed.
So at this point, it just seems like a nearly 100% increase in revenue!
Further, I've emailed them for support a few times, and I've had fast and helpful replies each time from David. I'm gathering that it's a small-ish company, which I tend to prefer.
It's worth noting, though, that my site hasn't been made mobile-friendly yet (I've been working on it but it's taking forever), and when I ran a mobile sticky it raised less than $1 /day. So I took that off, but it may do better for mobile-friendly sites.
They pay on a Net 60 (like most), so I haven't gotten paid yet. But I've read several reviews, and no one has had any complaints about Sulvo so I'm not worried about that.
So far, though, I can highly recommend using Sulvo in addition to your Adsense!