According to my calculations that tank is closer to 2 US gallons. 7.6 liters.
Granted that, it's still a tiny tank.
If you're new to fish and shrimp keeping, it would be preferable to try this with a larger aquarium like a 38 liter or US sized 10 gallon.
But that's not saying you can't give it a shot with some hardy snails or few "cleaner" quality Neocaridinas. It's just too tiny for any fish, even a pair of feeder White Cloud Mountain fish would be pretty hard pressed to live comfortably within this tank. Nano tanks require some prior experience with aquarium keeping success.
The UK, being that most of it's land is on limestone, has a lot of GH and KH out of the taps. This means your water is going to be alkaline and although this is good for Ammonia>Nitrate conversion cycling, if the tank starts to build up ammonia even in small amounts
, it's going to stress the new creatures living within it. I'd pick up an API water test kit, possibly a TDS water conductivity pen, so you can check the water every half month or so.
The 5 watts consumption would be pump and light's total current draw, looking at the filter that comes with this tank it's a bit large for a tiny tank.
This tank seems like a better deal, it comes with a cover and it has more volume. It's nearly twice the volume. I'd ditch the neon colored gravel and plastic plant for some darkish substrate and a 25 watt controllable heater..https://www.therange.co.uk/pets/fish...ter-kit#535691
You're still going to have to source a small LED light. But a small book reading LED desk light with a flexible neck would be far better, even if it's 2 watts. Most LEDs are approaching 120+ lumens per watt. A simple 6500 Kelvin reading light would suffice and you could moderate the light by bending the neck further away from the top. The little tank's light would be a hassle to replace if the electronics running it get wet and stop working.
P.S. OK, I missed reading that you're experienced with pico reef-keeping. You're far more experienced with fussy little tanks than I am I'm going to say if you could keep a tiny reef happy, you've got the chops to make a 2 gallon or smaller freshwater tank thrive.. Sorry if I sounded a bit dismissive of the size of the little tank.