I've exclusively bought mechanical keyboard related things from here, but i have had to pay customs charges for all but one order.
Charges have varied between £11 and £45
There are two places that deal with customs charges afaik, royal mail directly or a company called CCL (Customs Charge Limited).
One thing to watch out for is that for some reason massdrop uses a random internal email address for customs notices and does not forward this on to the user, CCL in particular only sends an email about charges so unless you are manually keeping track of the parcel, you never get this notice and the parcel is returned or lost without you ever knowing.
I find tracking the parcel and calling CCL directly with the order number is the only way to resolve this.
If its royal mail who are dealing with the charges i normally get an actual letter, so i can pay them as normal.