Unfortunately, the web site just says:
"AcuRite.com is currently unavailable in most European countries. We are engaged with the issue and committed to looking at options that support our full range of digital offerings to the EU market. We continue to identify technical compliance solutions that will provide all users with our time, temperature, and weather solutions."
This is despite the UK not being in the EU market!
Hakki, could you tell us if there is a model number for this? Then I could try it on Amazon.
I can thoroughly recommend the Govee room thermometer/hygrometer which was accurate to 2% RH (within the range we are interested in) out of the box and is a data logger which pairs with a phone app as well. Having a conventional hygrometer is of relatively limited use because you don't look at it very often but you get pretty graphs showing how RH varies with time and seasons if you have this.
Alternatively if you don't want a logging facility it is worth considering the Inkbird humidity controller. That has an accurate hygrometer and high/low power outputs so you can connect it to humidifiers and stuff for a DIY damp chaser or whole room equivalent.
Both of those are available on Amazon.
P.S. It isn't really necessary to calibrate either of these as they are accurate enough out of the box (it is after all swings in RH we are really interested in not the absolute value). But if you do set it use Potassium Carbonate to calibrate at 43%, if you calibrate with normal Salt at 80% the non-linearity of the instruments means that at the 40->50% we are really interested in the device will be *less* accurate than as originally supplied. That was the case for the three instruments I tested anyway. Also of note is that the hygrometer on the Meaco dehumidifier I have is surprisingly accurate and there is also a surprising difference between the RH at floor level and that on top of the piano. I can give you some Potassium Carbonate if you just want a small quantity for calibration.