I've tried MMO, Lucas, and now TCW3. I didn't like the Lucas product at all, especially the price of it. I feel I have best results with MMO, but I am continuing to experiment with TCW3, and haven't really voided it out yet.
TCW3 is much easier to OD an engine with, and a 500:1 ratio is about the most I'd run. MMO suggests a 320:1 ratio with their product.
In the winter time the engine seems to fire up faster and easier with a little MMO in the gas. I started TCW3 late in the season so I can't comment about winter starts. I also like the idea that a residual coating of oil remains in the cyl, especially for that first start in the morning.
My opinion is that MMO might keep things a little cleaner than TCW3, but TCW3 might offer slightly better compression. Both products are good, and I believe the benefits outweigh any possible dangers, providing you don't use too much of the product.