I won't trust that $30 hygro for the stated +/- 5% a simple hygro with that kind of spec will cost easily $300. What the package merely states is sensor accuracy and not system accuracy.
anyway i made a mistake. consumer hygros are accurate to +/-10% (range of 20%, i mixed up the +/- with the range) and many of the readings drift with temp changes.
well.. both meters are in your range of 45-55 unless you're really so uptight about that 1% difference of the gospel 45-55%.
OT: cigars otoh are more sensitive and demanding towards humidity because they do absorb or dry up in the environment they are stored. Some cigar collectors actually put in a humidifier inside a dry cab to maintain the humidity level to a +/- 1% difference. You might want to consider those dry cabs if you're worried about rubber cracking etc.
My dry cab ran at <30% for as long as I knew it and never had any of my lens, cameras or what nots inside cracked.