It works brilliantly and our patch does them as a one of for free to show the carp in the plated to demonstrate how a powerflush / magnaclean is a genuinely needed upgrade on a specific job.
Sonic cleaning is not new, I went for a job 20 years ago at a company who used it for cleaning (and jointing) industrial equipment. It is well proven.
it can obviously be a worthwhile piece of equipment for BG as the man hours Vs parts cost is a no brainer for them. For the independant its useless. The only thing that concerns me is the price, which if it is £250 and I'm assuming this is unconfirmed is insane. I would powerflush the whole boiler, system and plate heat exchanger for 40% more than that and guarantee the whole system against sludge problems for 3 years.