Pretty much all the gizmo's attached to cars in the past 15 years that are designed to distract the driver and feel like they're driving their armchairs with a TV remote in front of them. Generational safety technology peaked years ago with Stability and Traction Control, ABS, Impact protection and Air Bags. Now it's all big touch screens filled with information you don't need to know, that takes them vital milliseconds of response time away which could mean the survival of others.
A wired thing (some kind of rubber/ plastic contraption from memory) I tried a few years ago before a tour, that attached to the rear hub and was supposed to charge your phone/ Garmin or whatever as you went along. It disintegrated after a few miles. I was sad because it was a very thoughtful gift from my wife. It worked fine for the first 10 miles or so!
There's new technology that I've not tried, but have discounted as having very little benefit for me and would cost too much to upgrade. This includes tubeless, disc brakes, carbon fibre frames,
Technology which I have tried, but not convinced in benefits are
External bearing BB's - have gone back to square taper.
Gears for time trials - after a few seasons of riding both gears and fixed, have ditched the gears and just ride fixed. The difference between the two set ups was negligible.
Carbon tri spoke front wheel - lovely wheel, but so difficult to handle in cross winds, so have gone back to a "normal" front wheel.