I've just done the same, since my last order from them the other week got hit with customs, despite it being marked at $20.
What value did you request mate? I asked them to mark it with $15, just to be extra safe!
I asked them to mark value at $22 = €18.00
Rep of Ireland Import Threshold is €22
I could get away with been marked $30 based on today's exchange rate as that would work out at €24.54 with Vat been €5.64
Rep of Ireland Revenue (Customs) If the VAT payable is €6 or less it will not be collected
$20 = €16.00 in my experience with customs in Rep of Ireland with KimchiDvd/NovaMedia/Manta parcels is to low of a marked value so I ask for parcels be marked between $22-$25
It's not been an issue though with imports from USA when marked low
Ireland customs when it comes to imports from South Korea and Hong Kong If they suspect value is to low they will ignore the marked value and request a copy of PayPal Invoice
It's still down to luck though on the day with customs in Ireland as they random pick the parcels on the day
They did though select a good few of my parcels from South Korea and Hong Kong back in 2015 and 2016
I have been ok so far in 2017 but that might be because I was not importing much from South Korea compared to previous years
I only got hit once by customs in 2017