Annaraml. I am another who fell for that SparkleBowl ad, in lock down boredom. It was expensive and took ages to arrive.
When it didn't work as shown in the ad, I emailed the company, who replied that 'your loo has to be really dirty for it to work'. Not just normal staining.
(In the ad, the product foams right up to the rim of the bowl, in real life, it doesn't).
So, another lesson learned. 
I have found the very thick limescale remover, in the black bottle works.
Does anyone else think that the ceramics used in modern day toilets, are not as long lasting as in 'the olden days'?
I am sure the limescale builds up much faster.