I bought a Taylor 814e-N (sadly not from Thomann as they don't sell these fine guitars) and the Planet Waves humidity control product was recommended. So I bought some from Thomann.
Basically, I live in England where the climate is largely very wet, so the apparently most frequent problem - dryness - is not an issue for me specifically. In fact, our house is normally around 70% humidity - which is really high for quality guitars, which tend to expand and distort as the top in particular grows with moisture. Not good. So the humidity control for me is to lower the humidity inside the case to around 45% - which is perfect, and matches the situation in the factory where it was built.
Pros? It really works and is a convenient way to create a microclimate in your hard case that protects and preserves your fine instrument.
Cons? Not fair really to criticise something that works really well, but without a hygrometer you can't tell if it's working or not, so it would be cool if it had a colour strip that showed the relative humidity. Big ask, so really this is a cool product as is.
