Erhem! - to "return to topic", being the proud owner of a top bar hive (and a Warré too), I've gone for the most "natural" wood treatment I can find - boiled linseed oil with some beeswax melted into it, applied hot - if you use "Rustin's" linseed, it's not only completely safe, it's "food grade" too...... I suspect it's somewhat cheaper than proprietary chemicalised gubbins, smells splendid, and is completely harmless to bees, and the person applying it. It also works very well, used it for some years on sheds etc
Tbh more natural? - somewhat akin to a fallen hollow log - allows them to "do their own thing"..... as for Phil, I count him as a friend, never found him any less than charming, helpful, very knowledgeable, passionate and articulate......