Fair enough. Would be a hard sell to spend 1/4 of my time away from family though.

If I may ask do you pay for the travel or do you get reimbursed by your employer?

I can't imagine any scenario where a company is requiring monthly travel and not reimbursing for it.

And even assuming 1 full travel day on either side, 4 days a month is a LOT less than 1/4.

I think you missed the point, it's about distances, and logistics, not days. Flying from UK to NL/DE doesn't sound particularly impressive: relatively short, non-hostile checks, accessible airports, wide selection of flights. Actually, it's more or less equivalent to getting to Bilbao from Iberian peninsula area.