Yep, it's essentially the same as the additives that gets put in premium diesel, just means you can buy standard good quality diesel and make your own premium diesel for less. 3p a litre of diesel Vs the 10-15p premium of something like Shell V Power.
I use a bottle about every 5000 miles, so it's broadly the same spend as adblue.
So think of it as more of a preventative measure than a treatment.
Does it work? Well I have 245k diesel XC70 on the drive that still runs very well and smoke free (just don't ask about the ABS or the heater at the minute!) and I have a friend (who recommended it) with a 7 series BMW well into 300k.