I just tried it, and it seemed to work exceedingly well. I did not even have to pay anything, because this was a very small transaction, byte-wise, one input, one output, without change, so I could not use CPFP (Child Pays For Parent).
I had sent a transaction with 6 satoshi/byte by mistake. I used Electrum on Android and had earlier set the fees low (within 10 blocks), but had dynamic fees activated.
Some time before I sent the transation the mempool started to swell, and Electrum apparently did not react to this in time. The required fees were now around 150 satoshi/byte.
So I looked into this thread, found the link to
https://confirmtx.com/ and tried it. To my surprise the transaction got confirmed within a few blocks.
It seems highly likely that the transaction accelerator did it, because under normal circumstances at the current situation a 6 satoshi/byte transaction stands no chance to get confirmed.
Thanks for the nice tool. I hope it keeps working.