There's no bit in the thread about fitting a pump for an electric shower. One wouldn't be required for an electric. That's where fussy britches decided to get his tuppence worth in.
The op HAD an electric & wanted to change to a thermostatic mixer shower.
I can't remember seeing that post at all. But that's what confused me.
An electric is mains cold, therefore mains pressure - No pump required
Power Shower you can't put mains through or you'll blow the seals. Tank fed only
And the whole mixer thing really confuded me. Any mixer tap or shower valve that meets
regulations for the UK (not europe but UK, i.e WRAS approved) mixes at the spout and not in the body, they generally all come with check/non return valves built in to prevent cross flow. They also come with flow limiters to prevent too much back flow pressure when not in use. Most mixers nowadays will work from 0.1 bar so if it's up against 1.5 bar main, the right flow limiter will mean it works. So there's not always a need for a pump at all on the hot. Unless you
want a harder shower.
But the back flow and water peeing out the headers overflow is generally a myth these days. Unless your buying cheap, foreign brassware or not installing correctly.
From what i saw in that post, and i skimmed over most and concentrated more on yours and Trevs posts. There'd be no problem fitting a shower booster on the hot tank feed. It's better to be fair as your matching the main set by the water board and putting less strain on the valve. IMO