I'm not sure about Finland, but in the UK, normal international incoming registered/signed-for mail is not trackable unless for some reason (and it has happenned to me) it gets passed onto a local courier for deliver (eg Parcelforce 24/48 if Royal Mail deem the package too large for normal delivery).
From my experience with Ray, he sends normal USPS Airmail. It will take a bit over a week to deliver as the expected delivery time is 4-10 days (more like 9-10 days to the UK, in my experience). I guess you could ask him to send by USPS Global Priority, which has consistently delivered in exactly one week from postal date OR USPS Global Express EMS, which was delivered by ParcelForce 24 four days after dispatch (one or two days quicker than USPS GPM) and is fully trackable.
While others have had problems with USPS Global Express Mail, I've had nothing but very fast deliveries, the thought of ordering your item on Monday and getting it on Thursday or Friday is very nice. It's pretty costly, but reasonable (53USD for a 4kg amp, 30USD for a pair of headphones)
Ray tends to overestimate the delivery times. He quoted similar ones for both my transactions with him and they ended up coming in just over a week.