Are blind spot mirrors worth fitting, I refer of course to the small rimless mirrors that are stuck onto the existing wing mirrors.

I think they might help with reversing but have no experience of them. 

For the little they will cost just buy them and see.  Skoda do an electronic BLIND SPOT DETECTION WITH REAR TRAFFIC ALERT system which on the face of it seems brilliant but may well be an expensive disaster.  Skoda are "Simply clever" when it comes to charging for extras which are not simple to use.

Regarding the BLIND SPOT DETECTION WITH REAR TRAFFIC ALERT system, this forum thread may be of interest (and perhaps entertain!)

 

https://www.briskoda.net/forums/topic/518083-rear-traffic-alert-blind-spot-monitor-currently-unavail/

 

This 2022 Parkers review of  blind-spot mirrors may also be useful

 

https://www.parkers.co.uk/car-advice/product-reviews/best-blind-spot-mirrors/

 

and this product gets generally good Amazon reviews

 

https://www.amazon.co.uk/Blind-Spot-Mirrors-Cars-360°Rotatable/dp/B0777FXZY2#customerReviews

 

One thing to beware of is that, if the adhesive retaining 'pad' is a genuine 3M product, it may be a helluva job removing the blind-spot mirror from the original mirror's glass.