[hvalentim]

Having ±5% would be fine for this price class, but 10 - 30% is not.

True. But I did pay 10 times the price of one of these for a Sensirion SHT15 which ended up with that sort of offset after just eight months outside.

Of course, being of Chinese provenience one has always the suspicion it could be a second grade product.

But if you do a search you will find plenty of complaints of Davis users ending up with humidity offsets in their Sensirions as well...

I fear that for a reliable lasting measurement something like the Vaisala you suggest may be the only option.

Short of that, perhaps paying a bit more and getting the Sensirions from a reliable electronics store would be wise.