Some would hate the Baztan in Winter, some would hate walking in Winter...
I walked the Baztan (solo) in 2nd week of Jan this year, then again in April with a friend - loved them both,but different.
The Baztan is totally doable in Winter, as in any other route - as long as common sense is applied (which ain’t that common anymore...) I grew up with «
Fjellvettreglene» - the most important, in my mind, is 8- Don’t be ashamed to turn around/back.
There was fairly poor weather forecast on the day I started from Elizondo, so my plan was to walk 4-5 hours, then turn around - get the bus to Pamplona, but the weather shifted - and it was beautiful clear skies, so I carried on.
I had «mini-crampons» in my bag- needed them getting to airport from home - I used them once - crossing Belotea, and felt much safer; there’s a brook from the Ermita that had frozen, and the brook sort of covers the main path, crampons allowed me to «walk» down it. It might be doable without, but it’s plain stupid not to have them.
I started walking in January with short notice - accomodation was more limited than in peak season, but there were options available for days around the 20 and 30 km mark, most days also had an option for 12-16km. I had a down 3 season sleeping bag, would not have wanted to be without it - as I stayed in a few places with no/limited heating.
If you feel drawn to the Baztan - and are flexible enough to change plans according to weather - I see absolutely no reason why you should not choose it.
I know some have been disappointed about markings, paths, facilities - we all have different expectations. I am totally a Baztan «fan-girl». I love it! Feel free to PM,
best wishes for upcoming walk,