Actually, I was referring to Netsurf in general, not a specific implementation (I assume the rendering engine is the same for all forks and versions?). 
It depends what you mean by "rendering engine".

The layout engine is the same on all versions, however the bit which puts it on the screen is platform specific. For the AmigaOS 4 frontend, this uses graphics.library for drawing lines and things (with support for palette-mapped screenmodes too) and BulletAPI (diskfont.library) for text. Images that aren't in formats that NetSurf supports natively, are loaded using DataTypes.
The end result looks pretty much the same on all platforms if you ignore the GUI elements. Have a look at the screenshots on
http://www.netsurf-browser.org.
As for whether it is good enough for general browsing, I use it as my primary Amiga browser as it is so fast. Javascript support is very primitive at the moment, so pages that absolutely require Javascript won't work, but the majority of sites I visit are fine.