1 bed flat, no gas, under sink water heaters to replace immersion tank?

I own a1 Bed flat runs on eco 7, storage heaters, with a shower that heats water instantly. theres no room to really put a bath in so thats not an issue.
So It makes sense to fit a small instant tank (like an under sink type thing) in the kitchen, and one in the bathroom.
id like to put the one in the bathroom in the loft though directly above the basin, (just how important is it to Actually put it under the sink) as this is where the electrics are, and it will be well out of sight. so just…

1 bed flat, no gas, under sink water heaters to replace immersion tank?