It's unfortunate that the program is no longer being developed and so support is not available for it. Installation is fairly automatic and the open source PHP code is fairly easily modified, but you have to figure it out on your own.
We chose Webinsta in 2004 over other available programs because of its versatility and ease of use. Our organization continues to use Webinsta for its e-newsletter.
As open source, Webinsta allowed us to program a mySQL query to our main database which then creates the WebInsta list fresh whenever we send a newsletter. WebInsta supports sublists and multiple templates so we can send different looking newsletters to different groups.
One nuisance is the HTML preview of the message to be sent. It displays the text in gray rather than black so it doesn't give an exact representation of the output.
Perhaps because the code is dated, it doesn't have built-in support for DKIM, although I expect it will not be too hard to locate and add the DKIM key into the mail headers within WebInsta's code.
We often have newsletter editors who are not especially tech savvy, so the ease of composing and sending with WebInsta is crucial. WebInsta uses a 3-step process which is the easiest I've seen so far.
Overall, WebInsta is a great program for non-nerds to use, is easily customizable and can be installed and configured without much trouble. However, it is best installed and administered by someone proficient in PHP.