the opinels are good knives, and yes they do have pretty thin stock.
more importantly, they have a very thin edge, that if not careful, can be easily damaged. because of the full convex grind, they have no edge bevel to provide for a thicker sturdier edge.
when whittling fresh maple (no more than three weeks since cut) i did manage do put some small dings in the edge when i hit some of those tough dried out knots.
but, and this is a big but for me, using some sandpaper (100, 600, 1200) i got the dings out and restored the razor edge in under two minutes.
also, those dings occurred with the factory edge, with only a stropping. since taking some steel off, i have noticed the edge standing up better to hitting knots and things. perhaps i took off some of that decarburized soft steel from the edge that is often discussed.
i have never owned a buck, or have a desire to own one, because i personally disagree with the steel choice and the primary grind. but that is based on my own personal preferences, and you may like them for the same reasons i don't.
i also like the low cost of the opinel. the largest standard size they make costs about $15 most places. i think i have also seen a giant foot long version offered for sale somewhere, but i don't know that these are authentic.
i have also used some more traditional pattern slipjoint knives with great success in the woods, including the Case trapper in CV steel (with the yellow plastic handle scales to help prevent loss, which they have once so far)