Is this still a thing?

[joniboini]

People use these when they try to cheap out and their trans gets stuck, so they'll throw a few buxxx to give it a bump and a pickup. 

I'm not sure if it's related to zero-fee transactions quoted in your post, though. Those paid accelerators basically mean they spend more money to get their tx included in the next block, not making a 0 fee tx to the mining pool address if I'm understanding it correctly. Even the free accelerators are just rebroadcasters (or have a limited spot if it's done by the mining pools themselves).

[GhostRider25]

yes they re broadcast but what many do is, they are a mining pool.  your transaction is stuck, because you didn't pay enough to get it picked up. you pay them 'more' money, they'll make sure they pick up your transaction and include it in their next block find and process it.  your extra payment goes to them for picking up your transaction to include in the block.

think of it as a way to sort of go back in and 'boost' your fee you paid in a roundabout way.

Aaron

[WhoYouCantKill]

Is this still a thing ? Yes, it is and it will always be.
In theory it is always possible to perform a 51% attack on transactions with a single confirmation and it keeps getting harder as the number of confirmations increases.
But practically speaking, we need a huge amount of resources to do this and that involves a huge amount of investment.
On top of that, reversing that transaction won't be of any profit to the person doing it.

In this essence that the number of confirmations increases,  most people are the cost on why they do fall a victim of circumstances, because they fail to ask questions in any area they don't understand. There are some scammers that do use this medium to scam people 9f their funds and frankly speaking, they do this only daily which people are patronising them due to lack of proper information that they failed to get, that is why in everything that concerns transactions, people should not forget to ask questions and do the necessary thing for their own good.