I used ViaBTC free accelerator last week and it worked fine at that time although I had 2 failed attempts before a successful submission. I haven't used them in the last few days.
Total Accelerated Transactions:
702101
Let us see if it's going to change or there will be added transactions from that number within the next hours after I post this.
It will get changed because they do offer free acceleration but read what hosseinimr93 has shared. Ordinal spammers are abusing through the help of some automated tools to submit low-fee txs; there's no way we can beat automated tools LOL.
But acceleration service is always more expensive but Mempool offers it effective rate compared to Binance and viabtc but still RBF is way lot cheaper than using a paid accelerator but this isn't about paid accelerator, just the free one which is only offered by Viabtc.
A paid accelerator is only useful when you need acceleration a lot of times. I don't know the fee of ViaBTC paid accelerator or mempool though. Regardless, it can still be beneficial when you have a lot of txs to accelerate. Otherwise, it's a waste of money.