A while back I installed OctoGraph which pulls in your Octopus consumption as far back as it goes and compares it to Agile. I was on Go at the time, and going all the way back to late 2019, for any date range I chose, Agile was always cheaper, usually by £1-2 per day. This is through winter and spring (summer hadn’t started).
The way I think about Agile is that with every other tariff the energy company is hedging and they will always hedge very conservatively (meaning you pay fully for that hedging) whereas with Agile you are paying cost+ (where the + bit is fixed). Seems much fairer to me.