Taking the liberty of pinching their image for discussion purposes.

650kr is about £80 according to XE :
https://www.xe.com/currencyconverte...m=DKK&To=GBPI'm guessing about £100 with fees then. Sorry my mind only works in £s !
None of them have a very distinct Maltese Cross (MX). Red MXs are generally more popular than black.
The left most stamp looks in nice condition and has what I would class as good margins (from what I learn from Stanley Gibbons' guide). The cut touches the bottom of the frame, so arguably only 3 margins. Everyone has their own idea about that!
Second from left is very messy and badly toned - the toning could possibly be helped by bathing it in warm water, but the cancel kills it for me.
Third from left is really only about 2 clear margins at a generous push, but you can see the design quite well - it does have surface faults though too and is toned as well.
Fourth one really has no margins.
This does not take into account the plate numbers of course, just eye appeal and condition.
Even so, I think the "CC" is nice and the others could likely sell for £20-30 each as space fillers - it's the kind of quality I observe on
ebay for that kind of price.
I think I would pay about £60 (500kr) maybe a little more for the "CC" in auction.
Of course, we don't see the back view, so there could be pinholes, thins, tears, repairs etc.
So roughly speaking I don't think that the price paid is unusual really and like I said you have plate numbers that might make it more of a bargain.
These are just my own thoughts and interpretations.