I love gadgets and have been an early adopter of all sorts of gadgets and tech - I learned my lesson and am a lot more cautious these days.
I bought a Betamax. Fantastic bit of kit so not a total failure but of course short lived.
I bought a video recorder that used the remote control to control to scan a barcode printed in the newspapers tv listings to set the record timer function - remember what a faff it was to input the date, channel, time on / off on manually? Of course the scan function didn't work very well and was soon phased out (I think it was a Panasonic, I know it was expensive).
A rotisserie to cook chicken was so dangerous that it caused a nasty burn and soon went in the bin - it could only handle very small chickens.
I bought a Pocket Surfer in 2008/9- I think I was the only one that fell for the blurb. For those interested it is this
https://www.cnet.com/tech/computing/pocket-surfer-2-free-mobile-internet-unbelievably-fast/
All sorts of kitchen, garden, tech gadgets have promised so much and delivered so little.
What amazing gadget have you bought and been sorely disappointed with?