Sitegainer shines when it comes to being a very simple AB testing platform. The editor, though not without flaws, can be used by any member of a team, regardless of development knowledge. The AB tests seem to track properly, and there isn't much of a discrepancy in terms of numbers.
Sitegainer also offers heatmaps for clicks and scrolling on your landing pages. What I liked about sitegainer's heatmaps when compared to the ones offered by Hotjar, is that when you manipulate JS elements on your page (such as expanding a window) the clickmap follows.
Where the company does best is through its customer support. I've had them answer emails at all hours of the day, often within minutes of sending them. They have always accepted calls from us in order to tackle a tough issue or set up a certain feature. They even design entirely new features just because we've requested them.
As mentioned above, their editor is not the strongest option out there. As far as features go, it's got everything that you would need, it just tends to be a little bit buggy. It shows up on the page even when you aren't using their site (just clear your cache). It also doesn't handle moving elements around very well without the use of CSS or JS.
We needed a proper solution for AB tests, and they seemed to fit the bill. Their biggest benefit is that anyone can use it, regardless of technical knowledge.