If i have cydia, do i need installer?

You should keep them both. It’s like comparing FF and Safari, they both do the same thing in most aspects, but they come with different features and packages. Sometimes if you download sources to get more stuff like themes and whatnot, certain sources will only work with installer, and some will only work with cydia.

No, installer sucks.

Installer doesn’t suck. Get more sources.

I’ve had too many problems with it. Packages will install halfway, they won’t uninstall, they will say that they uninstalled when they didn’t. Its just too much of a hassle. Cydia works, and more people support it since Firmware 2.0 than Installer.