I wouldn't trust a single word British Gas say, that's not to say it isn't scaled or sludged up.
We all know British Cash have done a deal with a certain "Hydroflow 38" anti scale gadget, and we also know their sales sharks are going to push them at every opportunity, whether you need one or not.
Having said all that I like the Hydroflow 38, and the biggest concern with the Intergas combination boiler I have just installed at home was indeed scale in the secondary pipework, so I have one being trialed.

The only problem is, I will only know whether they work or not, if it doesn't scale up over the next 4-5 years, however you can be sure the world and his wife will know about it, if it doesn't work, assuming I'm still alive and kicking.

Incidentally they can be purchased on eBay for around £80, against BG £200.00

just clip it on the cold feed to the boiler and plug it in, Wow !!!