I used the last one, the one called Nygammal Ladersmorjning you can buy from Vildmarks hornan, for around 30 years
The boots I have been using since -79 until last year, RedWing Irish Setter boots, first I used RedWing Mink oil and RedWing Mink fat. Then after about one year I switched to that fat, after a Mink Oil, ( not RedWing brand).
I used the boots daily for three years, then every week a couple of days.
Having said that, I used a home made fat too, with more birch tar than the commercial products.
The boots were almost red when I bought them, and as I was in the Armed forces, it was not the correct colour, so the first week I used a high tar mix, to darken them.
I followed a regime the first week my dad taught me.
Sounds horrible, but here it is:
You wee inside the new boots, and make them really wet. You wear them daily until dry. Takes about a week.( Then the high tar fat outside to darken then as I wrote). Oil, wax product.
I had to replace the soles 2 times, to original Vibram soles.
The reason I had to stop wearing the boots is that my knee can not take the weight of the boots anymore.