Hey Martin, Yes Instapage is really good alternative to Leadpages. A/B test of landing pages are required, when a marketer need to test and optimize the performance of their existing lading page. Using A/B split test; they can change and optimize different elements of landing pages and see how the changes can impact their conversion to get high return.
Unbounce also lets you create sticky bars for your site. These bright forms draw attention to the offers and help to get more conversions without paying for more traffic. The editor allows you to add pop-up windows (which are called overlays here) on exit, on arrival, after a delay, on a scroll, or on click. There are plenty of pop-up templates to choose from, and you may also customize them. This feature is not available with Instapage.