I heard the money first goes to the central bank so there could be delays in reaching the destination account.

Also for buying a house the prices are in USD, so you'd lose a lot in exchange fees: Your currency > Pesos > USD

I know of people who used Western Union money transfer but I then the fees are high so maybe no good for buying property.

But I don't really know - I always just cash machines..

How's this work for people on the pensioners and financiers visas? It seems the money needs to be transferred monthly.

To add to my last message, it needs to be transferred monthly and western union wouldn't work because I wouldn't be abroad to send the money, esp. pension money, etc...

It's sad but it's true..it's quite messy to send money to Argentina. You should justify and submit a lot of supporting documents to receive money from Abroad..
We used to send money (which is our salary) to Argentina quarterly for the last 3 yrs....and thank God we managed to do that. My father-in-law has to submit certifications that the money we sent is for a certain cause in Argentina...for instance, family support, property buying, project on-going etc..etc...
For your question regarding the financiers and pensioners on how they handle that ..I believe it's part of their benefits on having that kind of visa...as well as for the investors.
If your plan is to buy a house and send the money from Abroad...then your real estate agent for sure can handle such matters...