The only time you are likely to have a problem when your ebike is a bit dodgy is when
a) you are clearly doing far over the 15.5 mph limit with no effort at all on the flat - and the cops have some free time
b) you do something that causes an accident which then prompts them to check
c) you are riding in an area where there are a lot of apparently illegal ebikes and e-scooters around and there have been a lot of complaints. Hence, the cops end up doing a blitz on everything - and you get pulled up for a 'random' check
Riding along in a reasonable way in an area with few ebikes is always going to be pretty OK - it isn;t worth their time to randomly check any old ebike.
WHen I had my previous ebike I did wonder if I would get pulled up for having a throttle. As it was quite old it was legal by the pre 2016 regulations - but the chances of your average copper knowing that would be quite low!!
I'm not disagreeing with the practical aspect of your advice; however, we need to keep a proportioned view. For any pragmatist it's very much an over-statement. The word "likely" should be replaced by "unlikely".
Certain forum members are known to have spent a lot of time over the 15 mph limit without pedalling, but they never got prosecuted for it, and, apparently, nor did anybody
There was at least one forum member plus the guy that killed that woman, who had their bikes checked by the police after an accident. One wasn't charged and the other was found innocent by a jury. They're the only two examples I have. There are probably a lot more.
As far as (c) is concerned, nobody has been prosecuted, so it's just theoretical.
As an aside, I live at the end of a culd-de-sac. Opposite me is a small branch off it, which also has a small brach off it, so it's sort of like a letter h. I'd noticed a kid about 7 years old riding a go-kart from time to time. A couple of days ago, I looked out of my window and saw that there were 4 very small kids all with similar go-karts having a race doing laps in the last branch and turning in the branch opposite me, which is where I could see them. It looked like a lot of fun. None of them were pedalling. It was difficult to judge the speed because I could only see them doing the 180 deg opposite me, but probably around 8 mph. The karts were quite small, so maybe something like this:
Yuanyan Kid Hoverkart, Air Cushion Cart, Electric Kart, Karting Bracket, Go-kart, with An Adjustable Front Wheel Bar/Two Steering Handles, Suitable for children for Self Balancing Training : Amazon.co.uk: Sports & Outdoors
www.amazon.co.uk
Should I knock on his door and ask him if he wants his kart hot-rodded?