Seen this advertised a lot on Facebook, just wondered if anyone on here has had it done on their mk1 Octy and how it was?

Do you mean terraclean or hydrogen treatment? The hydrogen treatment is more for diesels as it clears soot out of the intake system I believe. Terraclean is a nanotechnology clean for the fueling system, which also cleans the cat. I had a terraclean on my vrs, didn't notice much difference, v slightly better throttle response and mpg but nothing major.

Sounds like it yea. Not worth 100 quid then?

The Octavia shouldnt suffer from clogged valves etc as its not a direct injection engine.  If the engine is running fine and you put good fuel in, should be no need.

Sounds like it yea. Not worth 100 quid then?

I don't think so, as hinted at above just use vpower or similar. Put it towards a remap if you've not got one or some handling improvements...

I have noticed a difference in mpg after half a tank of v power as it goes. I was pretty surprised, thought it was just sales nonsense but it's taken me for 35mpg to 38mpg!

Nah vpower rules in those engines, some prefer momentum but not many. The car wants at least 97ron, 99ron is a massive bonus and a requirement for stage 1 remap really.