What you have there is the apple HPV (High Performance Video) card. There are two versions:
- 1MB of onboard VRAM, expandable to 2MB with 4 x 256k VRAM SIMMs
- 2MB of onboard VRAM, expandable to 4MB with 4 x 512k VRAM SIMMs
These are regarded as amongst the best available video upgrades for an x100 PowerMac, as they use a full 64 bit data path and are PDS (Processor Direct) rather than stuck on the Nubus bottleneck.
They also, as you can see, can be mounted on the fast side of a G3 upgrade, where they can make use of the much faster cache on the upgrade module.
As the onboard video in the x100 series uses main system RAM as VRAM ("vampire video") it is hideously slow compared to an AV, HPV or even most Nubus cards with dedicated VRAM.
Trash, that card is called the AV card, not the HPV. It's not as fast as the HPV, but as you say, it does give you S-Video in and out.
You can find out just about everything about these and related cards here:
http://kan.org/6100/graphics.html