Yes it's abandonware; yes it's not secure; yes you need to open a port and let it run for weeks / months; yes you can run into very questionable material, which you should delete right away. But you can still find stuff not available anywhere else and it's good for discovering new things (or should I say, old things.)
If you're still interested, I recommend: 1. encrypting the entire PC you dedicate to it; 2. using Linux + Wine instead of Windows if you have the skills to do so, otherwise use a non-spying version of Windows such as XP; 3. having an always-on VPN on that PC that lets you open ports; 4. leaving said PC always running, because the downloads are a long term business. You can use an old laptop or even a fanless mini-pc with no display or keyboard attached, left running in a closet or basement.
As for security, its communications are somewhat encrypted, but its model was always "security by obscurity," which you should know is not secure at all. The program follows in the steps of Winny, which follows in the steps of WinMX, for anybody who remembers them. Given it's questionable security, I recommend encrypting any PCs and hard disks that come into contact with it and always using it under a VPN.
I haven't been using it for months, but I can answer questions about the software itself.