I had a Cyclops fluid trainer for 6 years and used it for 50% of my training.

Bought a smart trainer last fall (Tacx Neo) and now I do 95% of my training indoors. It has had the biggest impact on my training by a long shot.

It cost a lot of money, so I use the hell out of it. It also makes following workouts effortless for the fact that you only have to pedal and can shut your brain off. Plus it's quieter, there's no tire wear, and it feels much better to ride on.