Unlike players such as Douglas and Marlon, who were strange signings and made no sense, Yerry Mina is an actual talent who has already proven a lot out in South America and also has experience playing for his country. So I don't see this one as being a strange signing or a risk, especially when you consider that he's not going to cost a ridiculous fee. He could well end up being a steal and I think he could adapt his game well to Spanish football, as talented Colombians seem to often do well there. It's all about him getting the minutes really. Umtiti is currently injured and it remains to be seen if Vermaelen(who is doing well lately, it has to be said) can stay injury free for the rest of the season, which is unfortunately doubtful when you consider his track record.
Either way, with Mascherano off, a 4th choice defender is a must and Yerry Mina will definitely get the pitch time I'd say. It might not work out for him, but there is definitely a strong possibility that it will and for the low price he will cost, it's not really a risk in a financial sense.
The Dutch league is terrible in this day and age and more players going from that league to the Spanish one seem to struggle more than ones going from South America, specifically the Brazilian and Argentine leagues.
Some players who have gone directly to Spain from South America and are still active:- Neymar, Aguero, Higuain, Marcelo, Dani Alves, Godin, Miranda, Casemiro, Filipe Luis...
Obviously it doesn't work for everyone, but there isn't a bigger risk buying players from Brazil or Argentina for a Spanish club than buying them from Holland, or even some of the other countries mentioned. Holland in the past was one of the breeding grounds for talent and some top players left for Spain(some very influential figures at that), but South America has always been a go to continent for talent when it comes to Spanish clubs. If not in Spain itself, then Brazil, Argentina, France and Portugal are great countries to find bargains and players that are suited to the Spanish game. Obviously England would be a great place to buy quality as it's ready made talent, but when Van Dijk is going for 75 million, it doesn't make sense to shop there.
England is a bit different due to the cultural differences, but players going directly from South America to Spain works out a lot and it has been common theme since even before Di Stefano's days.
As I mentioned in my post to Balon above, players such as Marlon Santos and Douglas didn't work out, but neither really came with high potential or after doing anything, they were simply outright nonsense signings and nothing was expected from either of them really. Mina on the other hand, is actually one of the stand out talents in Brazil right now, is already an international for Colombia and the price he will cost isn't ridiculous. It's worth taking the risk on him if you ask me.