I held off responding, deleted a few responses and left it a few days to rationalise. My view is we are not comparing like for like and using personal experience to say one thing is not worth the cost vs another, but we all want different things so it is good to have options. I have tried to open and fair on the costs below.
If someone can install this themselves, then paying £5850 for the linked AC battery is clearly cheaper but there is a value to the time you spend installing. Plus, you have to have wanted an AC battery, not a DC option, and have the ability fit it. This option will not allow you to have a newer export tariff (rather than on an estimated FIT) (unless you can sign off the paperwork yourself).
Comparing the battery part of the PowerWall with what I paid and adjusting the above £5850 to 13.5kW and we get £7140 (PowerWall inc VAT) vs £8313 (GivEnergy adjusted to 13.5kW inc VAT). That is without the Gateway which lets you disconnect from the grid in a power outage. Prices for the Powerwall will have gone up based on what we have seen (~13%) but assuming the Gateway and Battery increase is equal, the Powerwall battery is still similar price as the linked one above (£8068 vs £8313).
The Gateway is the significant extra and was £1008 in 2021 (inc VAT), assuming adjustment of 13%, £1139 now. This is a complete distribution board with dual phase feeds plus battery feed. It is a hub that communicates with central servers to allow them to charge and discharge the battery and gives the option to join the Tesla Energy Tariff. It is also one of only devices that I know of that is certified to disconnect your house from the grid so your house won't backfill to the grid harming local engineers, therefore it can stay powering your solar inverter in a power outage. Dropping this option is possible and will reduce the install cost.
My install cost £1440 (inc VAT) for Installation, testing, commissioning and notifications, plus delivery. 3 guys over 2 days, 2 dedicated electricians, call it 4 resource days.
If you can do your own install and it won't affect your export tariff, then self install is a good way to go. If you want certified, you are going to pay for install, if specialised work then you will pay more, I also paid more for the complexity of my property and the location of the battery and the Gateway. Each home install will be slightly different, there is no way my panels were going on in half a day, or my battery was being installed and commissioned the same day, so I paid extra for installation.