I have a cedar bar that spent the first 8 years of its life out in the elements. It's original Cetol finish is intact and looking good.
When someone says they are having issues with Cetol flaking off I am inclined to point to surface prep.
For teak, you need to get the oils away from the surface in order to get your first coat down in the wood. The wood's natural oils will prevent this.
I will always do an acetone wipe down, scrubbing the wood and changing rags often until I am getting no more "color" out of the wood onto the rags. This is my indicator that the oil is gone. Temporarily. Left alone, the remaining oils down in the wood WILL migrate back up to the surface.
VERY quickly after your wipe down, (as in only minutes or seconds) quickly apply your first coat. You want the finish to soak into the wood rather than lying on top.
Cetol has come a long way. You don't have to settle for the old translucent look any more. Here is the bar with the older formula:
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The service I have gotten from this now 15-year-old finish work tells me Cetol is indeed a good product.