Your friend's set up looks like a classic case for upgrading to a mains pressure cylinder. This could be much bigger than the existing cylinder, since it can use the space occupied by the storage tank as well, and can feed a decent shower directly.
In your case, where you have limited hot water capacity, heated by off peak electricity, an electric shower makes perfect sense, but ultimately, the best electric shower is a poor substitute for any decent shower fed by a hot water storage tanks.
Combi fed showers are better than electric ones, but still a long way short of a storage fed one.