I always go with extra layers of glass along the keel line. While glass is not as abrasion resistant as some synthetics, I find that 3 layers of 4 ounce e-glass will take years to wear through even with quite rough handling. By the time it wears through all sorts of other refinishing projects are over due.

I am not a fan of added keel strips that stick proud of the hull surface. For example the glass-tape and gelcoat abominations many people add to glass boats. The biggest source of drag for a boat moving through the water is frictional drag. A rough or uneven rub strip along the keel can add substantially to the frictional drag of the boat. Even if the surface of the strip itself is sanded perfectly smooth, a sudden surface change created by the edge of a rub strip will disrupt laminar flow adding a shocking amount of drag, they can also meaningfully effect the turning performance and maneuverability of the design.

I make a point of blending any additional layers smoothly into the bottom shape to maintain a fair and clean surface which minimizes any residual drag added to the hull shape. These extra glass layers tend to wear away smoothly and take years to wear through. Personally, I think a scratched up glass bottom looks better than synthetic strips stuck to the clear glass surface.

A couple extra layers of glass can provide years of protection and nobody need ever know they are there.