Hi Gene,
I switched to Le Tonk a few years back when I developed a reaction to pretty much everything else on the market. Seeing on how I have a wood boat I pretty much need to varnish some each year. I ran a test with Le Tonk on a picnic table that I slapped together from some old closet doors. I put ~8 coats on it and left it out for several years in the Colorado sun, snow, rain, etc. It still looked good after 3 years and didn't look bad until 4.5 years. The door members that made up the table top were tongue and groove. The grooves tended to pool water and that's where the varnish broke down first.
Here's a shot of my boat with Le Tonk on the deck. It's super easy to apply, doesn't smell like a toxic waste site, drys relatively quickly for varnish, and looks great. It's not quite as durable as the synthetics, but it works for me.